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POSTCONF(5)									      POSTCONF(5)

NAME
       postconf - Postfix configuration parameters

SYNOPSIS
       postconf parameter ...

       postconf -e "parameter=value" ...

DESCRIPTION
       The Postfix main.cf configuration file specifies a small subset of all the parameters that
       control the operation of the Postfix mail system. Parameters not specified in main.cf  are
       left at their default values.

       The general format of the main.cf file is as follows:

       o      Each  logical  line has the form "parameter = value".  Whitespace around the "=" is
	      ignored, as is whitespace at the end of a logical line.

       o      Empty lines and whitespace-only lines are ignored, as are lines  whose  first  non-
	      whitespace character is a `#'.

       o      A  logical line starts with non-whitespace text. A line that starts with whitespace
	      continues a logical line.

       o      A parameter value may refer to other parameters.

	      o      The expressions "$name", "${name}" or "$(name)" are recursively replaced  by
		     the value of the named parameter.

	      o      The expression "${name?value}" expands to "value" when "$name" is non-empty.
		     This form is supported with Postfix version 2.2 and later.

	      o      The expression "${name:value}" expands to "value"	when  "$name"  is  empty.
		     This form is supported with Postfix version 2.2 and later.

	      o      Specify "$$" to produce a single "$" character.

       o      When the same parameter is defined multiple times, only the last instance is remem-
	      bered.

       o      Otherwise, the order of main.cf parameter definitions does not matter.

       The remainder of this document is a description of all Postfix  configuration  parameters.
       Default	values	are  shown  after the parameter name in parentheses, and can be looked up
       with the "postconf -d" command.

       Note: this is not an invitation to  make  changes  to  Postfix  configuration  parameters.
       Unnecessary changes can impair the operation of the mail system.

2bounce_notice_recipient (default: postmaster)
       The  recipient  of undeliverable mail that cannot be returned to the sender.  This feature
       is enabled with the notify_classes parameter.

access_map_defer_code (default: 450)
       The numerical Postfix SMTP server response code	for  an  access(5)  map  "defer"  action,
       including  "defer_if_permit"  or  "defer_if_reject". Prior to Postfix 2.6, the response is
       hard-coded as "450".

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.6 and later.

access_map_reject_code (default: 554)
       The numerical Postfix SMTP server response code for an access(5) map "reject" action.

       Do not change this unless you have a complete understanding of RFC 5321.

address_verify_cache_cleanup_interval (default: 12h)
       The amount of time between verify(8) address verification database cleanup runs. This fea-
       ture requires that the database supports the "delete" and "sequence" operators.	Specify a
       zero interval to disable database cleanup.

       After each database cleanup run, the verify(8) daemon logs the number of entries that were
       retained  and  dropped.	A  cleanup  run is logged as "partial" when the daemon terminates
       early after "postfix reload", "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.7.

address_verify_default_transport (default: $default_transport)
       Overrides the default_transport parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_local_transport (default: $local_transport)
       Overrides the local_transport parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_map (default: see postconf -d output)
       Lookup table for persistent address verification status storage.  The table is  maintained
       by the verify(8) service, and is opened before the process releases privileges.

       The lookup table is persistent by default (Postfix 2.7 and later).  Specify an empty table
       name to keep the information in volatile memory which is lost after  "postfix  reload"  or
       "postfix stop". This is the default with Postfix version 2.6 and earlier.

       Specify	a  location  in a file system that will not fill up. If the database becomes cor-
       rupted, the world comes to an end. To recover delete  (NOT:  truncate)  the  file  and  do
       "postfix reload".

       Postfix	daemon	processes  do not use root privileges when opening this file (Postfix 2.5
       and later).  The file must therefore be stored under a Postfix-owned directory such as the
       data_directory.	 As  a	migration  aid,  an  attempt to open the file under a non-Postfix
       directory is redirected to the Postfix-owned data_directory, and a warning is logged.

       Examples:

       address_verify_map = hash:/var/lib/postfix/verify
       address_verify_map = btree:/var/lib/postfix/verify

       This feature is available in Postfix 2.1 and later.

address_verify_negative_cache (default: yes)
       Enable caching of failed  address  verification	probe  results.   When	this  feature  is
       enabled, the cache may pollute quickly with garbage.  When this feature is disabled, Post-
       fix will generate an address probe for every lookup.

       This feature is available in Postfix 2.1 and later.

address_verify_negative_expire_time (default: 3d)
       The time after which a failed probe expires from the address verification cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_negative_refresh_time (default: 3h)
       The time after which a failed address verification probe needs to be refreshed.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_poll_count (default: normal: 3, overload: 1)
       How many times to query the verify(8) service for the completion of an  address	verifica-
       tion request in progress.

       By  default,  the  Postfix SMTP server polls the verify(8) service up to three times under
       non-overload conditions, and only once when under overload.  With Postfix version 2.5  and
       earlier, the SMTP server always polls the verify(8) service up to three times by default.

       Specify 1 to implement a crude form of greylisting, that is, always defer the first deliv-
       ery request for a new address.

       Examples:

       # Postfix <= 2.6 default
       address_verify_poll_count = 3
       # Poor man's greylisting
       address_verify_poll_count = 1

       This feature is available in Postfix 2.1 and later.

address_verify_poll_delay (default: 3s)
       The delay between queries for  the  completion  of  an  address	verification  request  in
       progress.

       The default polling delay is 3 seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_expire_time (default: 31d)
       The time after which a successful probe expires from the address verification cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_refresh_time (default: 7d)
       The  time  after which a successful address verification probe needs to be refreshed.  The
       address verification status is not updated when the probe fails (optimistic caching).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_relay_transport (default: $relay_transport)
       Overrides the relay_transport parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_relayhost (default: $relayhost)
       Overrides the relayhost parameter setting for address verification probes.  This  informa-
       tion can be overruled with the transport(5) table.

       This feature is available in Postfix 2.1 and later.

address_verify_sender (default: $double_bounce_sender)
       The sender address to use in address verification probes; prior to Postfix 2.5 the default
       was "postmaster". To avoid problems with address probes	that  are  sent  in  response  to
       address	probes,  the Postfix SMTP server excludes the probe sender address from all SMTPD
       access blocks.

       Specify an empty value (address_verify_sender =) or <> if you want to use the null  sender
       address.  Beware,  some	sites  reject  mail  from  <>, even though RFCs require that such
       addresses be accepted.

       Examples:

       address_verify_sender = <>
       address_verify_sender = postmaster@my.domain

       This feature is available in Postfix 2.1 and later.

address_verify_sender_dependent_default_transport_maps (default: $sender_dependent_default_trans-
       port_maps)
       Overrides  the sender_dependent_default_transport_maps parameter setting for address veri-
       fication probes.

       This feature is available in Postfix 2.7 and later.

address_verify_sender_dependent_relayhost_maps (default: $sender_dependent_relayhost_maps)
       Overrides the sender_dependent_relayhost_maps parameter setting for  address  verification
       probes.

       This feature is available in Postfix 2.3 and later.

address_verify_sender_ttl (default: 0s)
       The  time  between  changes  in	the  time-dependent portion of address verification probe
       sender addresses. The time-dependent portion is appended to the localpart of  the  address
       specified with the address_verify_sender parameter. This feature is ignored when the probe
       sender addresses is the null sender, i.e. the address_verify_sender value is empty or <>.

       Historically, the probe sender address was fixed. This has caused such addresses to end up
       on spammer mailing lists, and has resulted in wasted network and processing resources.

       To  enable  time-dependent probe sender addresses, specify a non-zero time value (an inte-
       gral value plus an optional one-letter suffix that specifies the time  unit).   Specify	a
       value  of  at  least  several  hours, to avoid problems with senders that use greylisting.
       Avoid nice TTL values, to make the result less predictable.  Time units are: s  (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.9 and later.

address_verify_service_name (default: verify)
       The  name of the verify(8) address verification service. This service maintains the status
       of sender and/or recipient address verification probes, and generates probes on request by
       other Postfix processes.

address_verify_transport_maps (default: $transport_maps)
       Overrides the transport_maps parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_virtual_transport (default: $virtual_transport)
       Overrides the virtual_transport parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

alias_database (default: see postconf -d output)
       The  alias  databases  for  local(8)  delivery  that are updated with "newaliases" or with
       "sendmail -bi".

       This is a separate configuration parameter because  not	all  the  tables  specified  with
       $alias_maps have to be local files.

       Examples:

       alias_database = hash:/etc/aliases
       alias_database = hash:/etc/mail/aliases

alias_maps (default: see postconf -d output)
       The  alias  databases  that  are  used  for  local(8)  delivery. See aliases(5) for syntax
       details.

       The default list is system dependent.  On systems with NIS, the default is to  search  the
       local alias database, then the NIS alias database.

       If  you	change	the alias database, run "postalias /etc/aliases" (or wherever your system
       stores the mail alias file), or simply run "newaliases" to build the necessary DBM  or  DB
       file.

       The  local(8)  delivery	agent  disallows  regular  expression  substitution of $1 etc. in
       alias_maps, because that would open a security hole.

       The local(8) delivery agent will silently ignore requests to use  the  proxymap(8)  server
       within  alias_maps.  Instead  it will open the table directly. Before Postfix version 2.2,
       the local(8) delivery agent will terminate with a fatal error.

       Examples:

       alias_maps = hash:/etc/aliases, nis:mail.aliases
       alias_maps = hash:/etc/aliases

allow_mail_to_commands (default: alias, forward)
       Restrict local(8) mail delivery to external commands.  The default is to disallow delivery
       to "|command" in :include:  files (see aliases(5) for the text that defines this terminol-
       ogy).

       Specify zero or more of: alias,	forward  or  include,  in  order  to  allow  commands  in
       aliases(5), .forward files or in :include:  files, respectively.

       Example:

       allow_mail_to_commands = alias,forward,include

allow_mail_to_files (default: alias, forward)
       Restrict local(8) mail delivery to external files. The default is to disallow "/file/name"
       destinations in :include:  files (see aliases(5) for the text that defines this	terminol-
       ogy).

       Specify	zero or more of: alias, forward or include, in order to allow "/file/name" desti-
       nations in aliases(5), .forward files and in :include:  files, respectively.

       Example:

       allow_mail_to_files = alias,forward,include

allow_min_user (default: no)
       Allow a sender or recipient address to have `-' as the first character.	By default,  this
       is  not allowed, to avoid accidents with software that passes email addresses via the com-
       mand line. Such software would not be able to distinguish a malicious address from a  bona
       fide command-line option. Although this can be prevented by inserting a "--" option termi-
       nator into the command line, this is difficult to enforce consistently and globally.

       As of Postfix version 2.5, this feature is implemented by trivial-rewrite(8).   With  ear-
       lier  versions  this  feature  was  implemented	by  qmgr(8)  and was limited to recipient
       addresses only.

allow_percent_hack (default: yes)
       Enable the rewriting of the form "user%domain"  to  "user@domain".   This  is  enabled  by
       default.

       Note:  with Postfix version 2.2, message header address rewriting happens only when one of
       the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received  from  a	network  client  that  matches	$local_header_re-
	      write_clients,

       o      The  message  is	received  from	the network, and the remote_header_rewrite_domain
	      parameter specifies a non-empty value.

       To get the behavior before Postfix version 2.2,	specify  "local_header_rewrite_clients	=
       static:all".

       Example:

       allow_percent_hack = no

allow_untrusted_routing (default: no)
       Forward	mail  with  sender-specified  routing  (user[@%!]remote[@%!]site)  from untrusted
       clients to destinations matching $relay_domains.

       By default, this feature is turned off.	This closes a nasty open relay loophole  where	a
       backup  MX  host  can be tricked into forwarding junk mail to a primary MX host which then
       spams it out to the world.

       This parameter also controls if non-local  addresses  with  sender-specified  routing  can
       match  Postfix  access  tables.	By  default,  such  addresses cannot match Postfix access
       tables, because the address is ambiguous.

alternate_config_directories (default: empty)
       A list of non-default Postfix configuration directories that may  be  specified	with  "-c
       config_directory" on the command line, or via the MAIL_CONFIG environment parameter.

       This list must be specified in the default Postfix configuration directory, and is used by
       set-gid Postfix commands such as postqueue(1) and postdrop(1).

always_add_missing_headers (default: no)
       Always add (Resent-) From:, To:, Date: or Message-ID: headers when not  present.   Postfix
       2.6  and  later add these headers only when clients match the local_header_rewrite_clients
       parameter setting.  Earlier Postfix versions always add these headers; this may break DKIM
       signatures that cover non-existent headers.

always_bcc (default: empty)
       Optional  address  that receives a "blind carbon copy" of each message that is received by
       the Postfix mail system.

       Note: with Postfix 2.3 and later the BCC address is added as  if  it  was  specified  with
       NOTIFY=NONE.  The  sender  will	not be notified when the BCC address is undeliverable, as
       long as all down-stream software implements RFC 3461.

       Note: with Postfix 2.2 and earlier the sender will be notified when  the  BCC  address  is
       undeliverable.

       Note:  automatic  BCC  recipients  are produced only for new mail.  To avoid mailer loops,
       automatic BCC recipients are not generated after  Postfix  forwards  mail  internally,  or
       after Postfix generates mail itself.

anvil_rate_time_unit (default: 60s)
       The time unit over which client connection rates and other rates are calculated.

       This  feature is implemented by the anvil(8) service which is available in Postfix version
       2.2 and later.

       The default interval is relatively short. Because of the high frequency	of  updates,  the
       anvil(8)  server uses volatile memory only. Thus, information is lost whenever the process
       terminates.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

anvil_status_update_time (default: 600s)
       How  frequently	the anvil(8) connection and rate limiting server logs peak usage informa-
       tion.

       This feature is available in Postfix 2.2 and later.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

append_at_myorigin (default: yes)
       With  locally  submitted  mail,	append	the string "@$myorigin" to mail addresses without
       domain information. With remotely submitted mail, append the  string  "@$remote_header_re-
       write_domain" instead.

       Note  1:  this feature is enabled by default and must not be turned off.  Postfix does not
       support domain-less addresses.

       Note 2: with Postfix version 2.2, message header address rewriting happens only	when  one
       of the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The  message  is	received  from	a  network  client that matches $local_header_re-
	      write_clients,

       o      The message is received from  the  network,  and	the  remote_header_rewrite_domain
	      parameter specifies a non-empty value.

       To  get	the  behavior before Postfix version 2.2, specify "local_header_rewrite_clients =
       static:all".

append_dot_mydomain (default: yes)
       With locally submitted mail, append the string ".$mydomain"  to	addresses  that  have  no
       ".domain"    information.    With    remotely	submitted   mail,   append   the   string
       ".$remote_header_rewrite_domain" instead.

       Note 1: this feature is enabled by default. If disabled, users will not be  able  to  send
       mail to "user@partialdomainname" but will have to specify full domain names instead.

       Note  2:  with Postfix version 2.2, message header address rewriting happens only when one
       of the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received  from  a	network  client  that  matches	$local_header_re-
	      write_clients,

       o      The  message  is	received  from	the network, and the remote_header_rewrite_domain
	      parameter specifies a non-empty value.

       To get the behavior before Postfix version 2.2,	specify  "local_header_rewrite_clients	=
       static:all".

application_event_drain_time (default: 100s)
       How  long  the postkick(1) command waits for a request to enter the Postfix daemon process
       input buffer before giving up.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

authorized_flush_users (default: static:anyone)
       List of users who are authorized to flush the queue.

       By  default,  all  users  are allowed to flush the queue.  Access is always granted if the
       invoking user is the super-user or the $mail_owner user.  Otherwise, the real UID  of  the
       process is looked up in the system password file, and access is granted only if the corre-
       sponding login name is on the access list.  The username "unknown" is used  for	processes
       whose real UID is not found in the password file.

       Specify	a  list of user names, "/file/name" or "type:table" patterns, separated by commas
       and/or whitespace. The list is matched left to right, and the search stops  on  the  first
       match.  A "/file/name" pattern is replaced by its contents; a "type:table" lookup table is
       matched when a name matches a lookup key (the lookup result is  ignored).   Continue  long
       lines by starting the next line with whitespace. Specify "!pattern" to exclude a name from
       the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_mailq_users (default: static:anyone)
       List of users who are authorized to view the queue.

       By default, all users are allowed to view the queue.  Access  is  always  granted  if  the
       invoking  user  is the super-user or the $mail_owner user.  Otherwise, the real UID of the
       process is looked up in the system password file, and access is granted only if the corre-
       sponding  login	name is on the access list.  The username "unknown" is used for processes
       whose real UID is not found in the password file.

       Specify a list of user names, "/file/name" or "type:table" patterns, separated  by  commas
       and/or  whitespace.  The  list is matched left to right, and the search stops on the first
       match. A "/file/name" pattern is replaced by its contents; a "type:table" lookup table  is
       matched	when  a  name matches a lookup key (the lookup result is ignored).  Continue long
       lines by starting the next line with whitespace. Specify "!pattern" to exclude a user name
       from the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_submit_users (default: static:anyone)
       List of users who are authorized to submit mail with the sendmail(1) command (and with the
       privileged postdrop(1) helper command).

       By default, all users are allowed to submit mail.  Otherwise, the real UID of the  process
       is  looked up in the system password file, and access is granted only if the corresponding
       login name is on the access list.  The username "unknown" is used for processes whose real
       UID is not found in the password file. To deny mail submission access to all users specify
       an empty list.

       Specify a list of user names, "/file/name" or "type:table" patterns, separated  by  commas
       and/or  whitespace.  The  list is matched left to right, and the search stops on the first
       match. A "/file/name" pattern is replaced by its contents; a "type:table" lookup table  is
       matched	when  a  name matches a lookup key (the lookup result is ignored).  Continue long
       lines by starting the next line with whitespace. Specify "!pattern" to exclude a user name
       from the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

       Example:

       authorized_submit_users = !www, static:all

       This feature is available in Postfix 2.2 and later.

authorized_verp_clients (default: $mynetworks)
       What  remote SMTP clients are allowed to specify the XVERP command.  This command requests
       that mail be delivered one recipient at a time with a per recipient return address.

       By default, only trusted clients are allowed to specify XVERP.

       This parameter was introduced with Postfix version 1.1.	Postfix version 2.1 renamed  this
       parameter to smtpd_authorized_verp_clients and changed the default to none.

       Specify	a  list  of  network/netmask patterns, separated by commas and/or whitespace. The
       mask specifies the number of bits in the network part of a  host  address.  You	can  also
       specify	hostnames  or  .domain names (the initial dot causes the domain to match any name
       below it),  "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced  by
       its  contents;  a "type:table" lookup table is matched when a table entry matches a lookup
       string (the lookup result is ignored).  Continue long lines by starting the next line with
       whitespace.  Specify  "!pattern" to exclude an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6  address  information  must  be  specified  inside  []  in  the  autho-
       rized_verp_clients  value,  and	in  files  specified  with  "/file/name".   IP	version 6
       addresses contain the ":" character, and would otherwise be confused with  a  "type:table"
       pattern.

backwards_bounce_logfile_compatibility (default: yes)
       Produce	additional  bounce(8) logfile records that can be read by Postfix versions before
       2.0. The current and more extensible "name = value" format is needed in order to implement
       more sophisticated functionality.

       This feature is available in Postfix 2.1 and later.

berkeley_db_create_buffer_size (default: 16777216)
       The  per-table  I/O buffer size for programs that create Berkeley DB hash or btree tables.
       Specify a byte count.

       This feature is available in Postfix 2.0 and later.

berkeley_db_read_buffer_size (default: 131072)
       The per-table I/O buffer size for programs that read Berkeley DB  hash  or  btree  tables.
       Specify a byte count.

       This feature is available in Postfix 2.0 and later.

best_mx_transport (default: empty)
       Where  the  Postfix  SMTP client should deliver mail when it detects a "mail loops back to
       myself" error condition. This happens when the local MTA is the best SMTP  mail	exchanger
       for a destination not listed in $mydestination, $inet_interfaces, $proxy_interfaces, $vir-
       tual_alias_domains, or $virtual_mailbox_domains.  By  default,  the  Postfix  SMTP  client
       returns such mail as undeliverable.

       Specify,  for  example, "best_mx_transport = local" to pass the mail from the Postfix SMTP
       client to the local(8) delivery agent. You can specify any message delivery "transport" or
       "transport:nexthop"  that  is  defined  in the master.cf file. See the transport(5) manual
       page for the syntax and meaning of "transport" or "transport:nexthop".

       However, this feature is expensive because it ties up a Postfix SMTP client process  while
       the  local(8) delivery agent is doing its work. It is more efficient (for Postfix) to list
       all hosted domains in a table or database.

biff (default: yes)
       Whether or not to use the local biff service.  This service sends "new mail" notifications
       to users who have requested new mail notification with the UNIX command "biff y".

       For compatibility reasons this feature is on by default.  On systems with lots of interac-
       tive users, the biff service can be a performance drain.  Specify "biff = no"  in  main.cf
       to disable.

body_checks (default: empty)
       Optional  lookup  tables  for content inspection as specified in the body_checks(5) manual
       page.

       Note: with Postfix versions before 2.0, these rules inspect all content after the  primary
       message headers.

body_checks_size_limit (default: 51200)
       How much text in a message body segment (or attachment, if you prefer to use that term) is
       subjected to body_checks inspection.  The amount of text is limited to avoid scanning huge
       attachments.

       This feature is available in Postfix 2.0 and later.

bounce_notice_recipient (default: postmaster)
       The  recipient  of  postmaster notifications with the message headers of mail that Postfix
       did not deliver and of SMTP conversation transcripts of mail that Postfix did not receive.
       This feature is enabled with the notify_classes parameter.

bounce_queue_lifetime (default: 5d)
       Consider  a  bounce  message as undeliverable, when delivery fails with a temporary error,
       and the time in the queue has reached the bounce_queue_lifetime limit.  By  default,  this
       limit is the same as for regular mail.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is d (days).

       Specify 0 when mail delivery should be tried only once.

       This feature is available in Postfix 2.1 and later.

bounce_service_name (default: bounce)
       The name of the bounce(8) service. This service maintains  a  record  of  failed  delivery
       attempts and generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

bounce_size_limit (default: 50000)
       The  maximal  amount of original message text that is sent in a non-delivery notification.
       Specify a byte count.  A message is returned as either message/rfc822 (the complete origi-
       nal)  or as text/rfc822-headers (the headers only).  With Postfix version 2.4 and earlier,
       a message is always returned as message/rfc822 and is truncated when it exceeds	the  size
       limit.

       Notes:

       o      If  you  increase this limit, then you should increase the mime_nesting_limit value
	      proportionally.

       o      Be careful when making changes.  Excessively large values will result in	the  loss
	      of non-delivery notifications, when a bounce message size exceeds a local or remote
	      MTA's message size limit.

bounce_template_file (default: empty)
       Pathname of a configuration file with bounce message templates.	These override the built-
       in  templates  of  delivery status notification (DSN) messages for undeliverable mail, for
       delayed mail, successful delivery, or delivery verification.  The  bounce(5)  manual  page
       describes how to edit and test template files.

       Template  message  body text may contain $name references to Postfix configuration parame-
       ters. The result of $name expansion can be previewed with "postconf -b  file_name"  before
       the file is placed into the Postfix configuration directory.

       This feature is available in Postfix 2.3 and later.

broken_sasl_auth_clients (default: no)
       Enable  inter-operability  with	remote SMTP clients that implement an obsolete version of
       the AUTH command (RFC 4954). Examples of such clients are MicroSoft Outlook  Express  ver-
       sion 4 and MicroSoft Exchange version 5.0.

       Specify	"broken_sasl_auth_clients = yes" to have Postfix advertise AUTH support in a non-
       standard way.

canonical_classes (default: envelope_sender, envelope_recipient, header_sender, header_recipient)

       What  addresses are subject to canonical_maps address mapping.  By default, canonical_maps
       address mapping is applied to envelope sender  and  recipient  addresses,  and  to  header
       sender and header recipient addresses.

       Specify one or more of: envelope_sender, envelope_recipient, header_sender, header_recipi-
       ent

       This feature is available in Postfix 2.2 and later.

canonical_maps (default: empty)
       Optional address mapping lookup tables for message headers and envelopes. The  mapping  is
       applied	to both sender and recipient addresses, in both envelopes and in headers, as con-
       trolled with the canonical_classes parameter. This is typically used  to  clean	up  dirty
       addresses  from legacy mail systems, or to replace login names by Firstname.Lastname.  The
       table format and lookups are documented	in  canonical(5).  For	an  overview  of  Postfix
       address manipulations see the ADDRESS_REWRITING_README document.

       If  you	use this feature, run "postmap /etc/postfix/canonical" to build the necessary DBM
       or DB file after every change. The changes will become visible after a minute or so.   Use
       "postfix reload" to eliminate the delay.

       Note:  with  Postfix version 2.2, message header address mapping happens only when message
       header address rewriting is enabled:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received  from  a	network  client  that  matches	$local_header_re-
	      write_clients,

       o      The  message  is	received  from	the network, and the remote_header_rewrite_domain
	      parameter specifies a non-empty value.

       To get the behavior before Postfix version 2.2,	specify  "local_header_rewrite_clients	=
       static:all".

       Examples:

       canonical_maps = dbm:/etc/postfix/canonical
       canonical_maps = hash:/etc/postfix/canonical

cleanup_service_name (default: cleanup)
       The  name  of  the  cleanup(8)  service. This service rewrites addresses into the standard
       form, and performs canonical(5) address mapping and virtual(5) aliasing.

       This feature is available in Postfix 2.0 and later.

command_directory (default: see postconf -d output)
       The location of all postfix administrative commands.

command_execution_directory (default: empty)
       The local(8) delivery agent working directory for delivery to external  command.   Failure
       to change directory causes the delivery to be deferred.

       The  following  $name expansions are done on command_execution_directory before the direc-
       tory is changed. Expansion happens in the context of the delivery request.  The result  of
       $name  expansion  is  filtered  with  the  character set that is specified with the execu-
       tion_directory_expansion_filter parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
	      The full recipient address.

       $extension
	      The optional recipient address extension.

       $domain
	      The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
	      The system-wide recipient address extension delimiter.

       ${name?value}
	      Expands to value when $name is non-empty.

       ${name:value}
	      Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       This feature is available in Postfix 2.2 and later.

command_expansion_filter (default: see postconf -d output)
       Restrict the characters that the local(8) delivery agent allows	in  $name  expansions  of
       $mailbox_command and $command_execution_directory.  Characters outside the allowed set are
       replaced by underscores.

command_time_limit (default: 1000s)
       Time limit for delivery to external commands. This limit is used by the local(8)  delivery
       agent, and is the default time limit for delivery by the pipe(8) delivery agent.

       Note:  if  you set this time limit to a large value you must update the global ipc_timeout
       parameter as well.

config_directory (default: see postconf -d output)
       The default location of the Postfix main.cf and master.cf configuration files. This can be
       overruled via the following mechanisms:

       o      The MAIL_CONFIG environment variable (daemon processes and commands).

       o      The "-c" command-line option (commands only).

       With  Postfix  command  that  run  with	set-gid  privileges,  a config_directory override
       requires either root privileges, or it requires that the  directory  is	listed	with  the
       alternate_config_directories parameter in the default main.cf file.

connection_cache_protocol_timeout (default: 5s)
       Time  limit  for  connection cache connect, send or receive operations.	The time limit is
       enforced in the client.

       This feature is available in Postfix 2.3 and later.

connection_cache_service_name (default: scache)
       The name of the scache(8) connection cache service.  This service maintains a limited pool
       of cached sessions.

       This feature is available in Postfix 2.2 and later.

connection_cache_status_update_time (default: 600s)
       How  frequently	the  scache(8) server logs usage statistics with connection cache hit and
       miss rates for logical destinations and for physical endpoints.

connection_cache_ttl_limit (default: 2s)
       The maximal time-to-live value that the scache(8) connection cache server allows. Requests
       that specify a larger TTL will be stored with the maximum allowed TTL. The purpose of this
       additional control is to protect the infrastructure against careless people. The cache TTL
       is already bounded by $max_idle.

content_filter (default: empty)
       After  the  message is queued, send the entire message to the specified transport:destina-
       tion. The transport name specifies the first field of a mail delivery agent definition  in
       master.cf;  the	syntax of the next-hop destination is described in the manual page of the
       corresponding delivery agent.  More information about external content filters is  in  the
       Postfix FILTER_README file.

       Notes:

       o      This  setting  has  lower  precedence  than a FILTER action that is specified in an
	      access(5), header_checks(5) or body_checks(5) table.

       o      The meaning of an empty next-hop filter destination is version dependent.   Postfix
	      2.7 and later will use the recipient domain; earlier versions will use $myhostname.
	      Specify "default_filter_nexthop = $myhostname" for compatibility with  Postfix  2.6
	      or  earlier,  or	specify a content_filter value with an explicit next-hop destina-
	      tion.

cyrus_sasl_config_path (default: empty)
       Search path for Cyrus SASL application configuration files, currently used only to  locate
       the  $smtpd_sasl_path.conf  file.   Specify  zero or more directories separated by a colon
       character, or an empty value to use Cyrus SASL's built-in search path.

       This feature is available in Postfix 2.5 and later when compiled with Cyrus SASL 2.1.22 or
       later.

daemon_directory (default: see postconf -d output)
       The  directory  with  Postfix  support  programs and daemon programs.  These should not be
       invoked directly by humans. The directory must be owned by root.

daemon_table_open_error_is_fatal (default: no)
       How a Postfix daemon process handles errors while opening lookup tables: gradual  degrada-
       tion or immediate termination.

	no  (default)
	      Gradual  degradation: a daemon process logs a message of type "error" and continues
	      execution with reduced functionality. Features that do not depend on  the  unavail-
	      able  table will work normally, while features that depend on the table will result
	      in a type "warning" message.
	      When the notify_classes parameter value contains the "data" class, the Postfix SMTP
	      server and client will report transcripts of sessions with an error because a table
	      is unavailable.

	yes  (historical behavior)
	      Immediate termination: a daemon process logs a type "fatal" message and  terminates
	      immediately.   This  option reduces the number of possible code paths through Post-
	      fix, and may therefore be slightly more secure than the default.

       For the sake of sanity, the number of type "error" messages is  limited	to  13	over  the
       lifetime of a daemon process.

       This feature is available in Postfix 2.9 and later.

daemon_timeout (default: 18000s)
       How  much  time	a Postfix daemon process may take to handle a request before it is termi-
       nated by a built-in watchdog timer.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

data_directory (default: see postconf -d output)
       The  directory  with  Postfix-writable data files (for example: caches, pseudo-random num-
       bers).  This directory must be owned by the mail_owner account, and  must  not  be  shared
       with non-Postfix software.

       This feature is available in Postfix 2.5 and later.

debug_peer_level (default: 2)
       The increment in verbose logging level when a remote client or server matches a pattern in
       the debug_peer_list parameter.

debug_peer_list (default: empty)
       Optional list of remote client or server hostname or network address patterns  that  cause
       the verbose logging level to increase by the amount specified in $debug_peer_level.

       Specify	domain	names,	network/netmask  patterns,  "/file/name" patterns or "type:table"
       lookup tables. The right-hand side result from "type:table" lookups is ignored.

       Pattern matching of domain names is  controlled	by  the  parent_domain_matches_subdomains
       parameter.

       Examples:

       debug_peer_list = 127.0.0.1
       debug_peer_list = example.com

debugger_command (default: empty)
       The  external  command  to  execute  when  a Postfix daemon program is invoked with the -D
       option.

       Use "command .. & sleep 5" so that the debugger can attach before the process marches  on.
       If  you	use  an  X-based debugger, be sure to set up your XAUTHORITY environment variable
       before starting Postfix.

       Note: the command is subject to $name expansion, before it is passed to the default  comm-
       mand interpreter. Specify "$$" to produce a single "$" character.

       Example:

       debugger_command =
	   PATH=/usr/bin:/usr/X11R6/bin
	   ddd $daemon_directory/$process_name $process_id & sleep 5

default_database_type (default: see postconf -d output)
       The  default database type for use in newaliases(1), postalias(1) and postmap(1) commands.
       On many UNIX systems the default type is either dbm or hash. The default setting is frozen
       when the Postfix system is built.

       Examples:

       default_database_type = hash
       default_database_type = dbm

default_delivery_slot_cost (default: 5)
       How often the Postfix queue manager's scheduler is allowed to preempt delivery of one mes-
       sage with another.

       Each transport maintains a so-called "available delivery slot counter" for  each  message.
       One  message can be preempted by another one when the other message can be delivered using
       no more delivery slots (i.e., invocations of delivery agents)  than  the  current  message
       counter has accumulated (or will eventually accumulate - see about slot loans below). This
       parameter controls  how	often  is  the	counter  incremented  -  it  happens  after  each
       default_delivery_slot_cost recipients have been delivered.

       The  cost of 0 is used to disable the preempting scheduling completely.	The minimum value
       the scheduling algorithm can use is 2 - use  it	if  you  want  to  maximize  the  message
       throughput  rate.  Although  there is no maximum, it doesn't make much sense to use values
       above say 50.

       The only reason why the value of 2 is not the default is the way  this  parameter  affects
       the  delivery  of  mailing-list mail. In the worst case, their delivery can take somewhere
       between (cost+1/cost) and (cost/cost-1) times more than if the  preemptive  scheduler  was
       disabled.  The  default	value of 5 turns out to provide reasonable message response times
       while making sure the mailing-list deliveries are not extended by more than 20-25  percent
       even in the worst case.

       Use transport_delivery_slot_cost to specify a transport-specific override, where transport
       is the master.cf name of the message delivery transport.

       Examples:

       default_delivery_slot_cost = 0
       default_delivery_slot_cost = 2

default_delivery_slot_discount (default: 50)
       The default value for transport-specific _delivery_slot_discount settings.

       This parameter speeds up the moment when a message preemption can happen. Instead of wait-
       ing until the full amount of delivery slots required is available, the preemption can hap-
       pen when transport_delivery_slot_discount percent  of  the  required  amount  plus  trans-
       port_delivery_slot_loan	still  remains to be accumulated.  Note that the full amount will
       still have to be accumulated before another preemption can take place later.

       Use transport_delivery_slot_discount  to  specify  a  transport-specific  override,  where
       transport is the master.cf name of the message delivery transport.

default_delivery_slot_loan (default: 3)
       The default value for transport-specific _delivery_slot_loan settings.

       This parameter speeds up the moment when a message preemption can happen. Instead of wait-
       ing until the full amount of delivery slots required is available, the preemption can hap-
       pen  when  transport_delivery_slot_discount  percent  of  the  required amount plus trans-
       port_delivery_slot_loan still remains to be accumulated.  Note that the full  amount  will
       still have to be accumulated before another preemption can take place later.

       Use transport_delivery_slot_loan to specify a transport-specific override, where transport
       is the master.cf name of the message delivery transport.

default_destination_concurrency_failed_cohort_limit (default: 1)
       How many pseudo-cohorts must suffer connection or handshake failure before a specific des-
       tination  is  considered  unavailable (and further delivery is suspended). Specify zero to
       disable this feature. A destination's pseudo-cohort failure count is  reset  each  time	a
       delivery completes without connection or handshake failure for that specific destination.

       A pseudo-cohort is the number of deliveries equal to a destination's delivery concurrency.

       Use  transport_destination_concurrency_failed_cohort_limit to specify a transport-specific
       override, where transport is the master.cf name of the message delivery transport.

       This feature is available in Postfix 2.5. The default setting is compatible  with  earlier
       Postfix versions.

default_destination_concurrency_limit (default: 20)
       The  default  maximal  number of parallel deliveries to the same destination.  This is the
       default limit for delivery via the  lmtp(8),  pipe(8),  smtp(8)	and  virtual(8)  delivery
       agents.	With per-destination recipient limit > 1, a destination is a domain, otherwise it
       is a recipient.

       Use transport_destination_concurrency_limit  to	specify  a  transport-specific	override,
       where transport is the master.cf name of the message delivery transport.

default_destination_concurrency_negative_feedback (default: 1)
       The  per-destination  amount  of  delivery concurrency negative feedback, after a delivery
       completes with a connection or handshake failure. Feedback values are in  the  range  0..1
       inclusive.  With  negative  feedback,  concurrency  is  decremented  at the beginning of a
       sequence of length 1/feedback. This is unlike  positive	feedback,  where  concurrency  is
       incremented at the end of a sequence of length 1/feedback.

       As  of  Postfix version 2.5, negative feedback cannot reduce delivery concurrency to zero.
       Instead, a destination is marked  dead  (further  delivery  suspended)  after  the  failed
       pseudo-cohort   count   reaches	$default_destination_concurrency_failed_cohort_limit  (or
       $transport_destination_concurrency_failed_cohort_limit).  To make the scheduler completely
       immune  to  connection  or  handshake  failures,  specify a zero feedback value and a zero
       failed pseudo-cohort limit.

       Specify one of the following forms:

       number

       number / number
	      Constant feedback. The value must be in the range 0..1 inclusive.  The default set-
	      ting  of	"1" is compatible with Postfix versions before 2.5, where a destination's
	      delivery concurrency is throttled down to zero  (and  further  delivery  suspended)
	      after a single failed pseudo-cohort.

       number / concurrency
	      Variable	feedback of "number / (delivery concurrency)".	The number must be in the
	      range 0..1 inclusive. With number equal to "1", a  destination's	delivery  concur-
	      rency is decremented by 1 after each failed pseudo-cohort.

       A pseudo-cohort is the number of deliveries equal to a destination's delivery concurrency.

       Use  transport_destination_concurrency_negative_feedback  to  specify a transport-specific
       override, where transport is the master.cf name of the message delivery transport.

       This feature is available in Postfix 2.5. The default setting is compatible  with  earlier
       Postfix versions.

default_destination_concurrency_positive_feedback (default: 1)
       The  per-destination  amount  of  delivery concurrency positive feedback, after a delivery
       completes without connection or handshake failure. Feedback values are in the  range  0..1
       inclusive.  The concurrency increases until it reaches the per-destination maximal concur-
       rency limit. With positive feedback, concurrency is incremented at the end of  a  sequence
       with length 1/feedback. This is unlike negative feedback, where concurrency is decremented
       at the start of a sequence of length 1/feedback.

       Specify one of the following forms:

       number

       number / number
	      Constant feedback.  The value must be in the range 0..1 inclusive. The default set-
	      ting  of	"1" is compatible with Postfix versions before 2.5, where a destination's
	      delivery concurrency doubles after each successful pseudo-cohort.

       number / concurrency
	      Variable feedback of "number / (delivery concurrency)".  The number must be in  the
	      range  0..1  inclusive.  With number equal to "1", a destination's delivery concur-
	      rency is incremented by 1 after each successful pseudo-cohort.

       A pseudo-cohort is the number of deliveries equal to a destination's delivery concurrency.

       Use transport_destination_concurrency_positive_feedback to  specify  a  transport-specific
       override, where transport is the master.cf name of the message delivery transport.

       This feature is available in Postfix 2.5 and later.

default_destination_rate_delay (default: 0s)
       The  default  amount  of  delay that is inserted between individual deliveries to the same
       destination; the resulting behavior depends on the value of the corresponding per-destina-
       tion recipient limit.

       o      With  a corresponding per-destination recipient limit > 1, the rate delay specifies
	      the time between deliveries to the same domain.  Different domains are delivered in
	      parallel, subject to the process limits specified in master.cf.

       o      With  a  corresponding  per-destination  recipient limit equal to 1, the rate delay
	      specifies the time between deliveries to the same recipient.  Different  recipients
	      are delivered in parallel, subject to the process limits specified in master.cf.

       To  enable  the	delay,	specify a non-zero time value (an integral value plus an optional
       one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w  (weeks).  The  default  time
       unit is s (seconds).

       NOTE:  the  delay is enforced by the queue manager. The delay timer state does not survive
       "postfix reload" or "postfix stop".

       Use transport_destination_rate_delay  to  specify  a  transport-specific  override,  where
       transport is the master.cf name of the message delivery transport.

       NOTE:  with  a  non-zero  _destination_rate_delay, specify a transport_destination_concur-
       rency_failed_cohort_limit of 10 or more to prevent Postfix from deferring all mail for the
       same destination after only one connection or handshake error.

       This feature is available in Postfix 2.5 and later.

default_destination_recipient_limit (default: 50)
       The  default maximal number of recipients per message delivery.	This is the default limit
       for delivery via the lmtp(8), pipe(8), smtp(8) and virtual(8) delivery agents.

       Setting this parameter to a value of 1 affects email deliveries as follows:

       o      It changes the meaning of the corresponding per-destination concurrency limit, from
	      concurrency  of deliveries to the same domain into concurrency of deliveries to the
	      same recipient.  Different recipients are delivered in  parallel,  subject  to  the
	      process limits specified in master.cf.

       o      It  changes  the	meaning of the corresponding per-destination rate delay, from the
	      delay between deliveries to the same domain into the delay  between  deliveries  to
	      the same recipient.  Again, different recipients are delivered in parallel, subject
	      to the process limits specified in master.cf.

       o      It changes the meaning of other corresponding per-destination settings in a similar
	      manner, from settings for delivery to the same domain into settings for delivery to
	      the same recipient.

       Use transport_destination_recipient_limit to specify a transport-specific override,  where
       transport is the master.cf name of the message delivery transport.

default_extra_recipient_limit (default: 1000)
       The  default  value  for  the extra per-transport limit imposed on the number of in-memory
       recipients.  This extra recipient space is reserved for the cases when the  Postfix  queue
       manager's scheduler preempts one message with another and suddenly needs some extra recip-
       ients slots for the chosen message in order to avoid performance degradation.

       Use transport_extra_recipient_limit to specify a transport-specific override, where trans-
       port is the master.cf name of the message delivery transport.

default_filter_nexthop (default: empty)
       When  a	content_filter	or FILTER request specifies no explicit next-hop destination, use
       $default_filter_nexthop instead; when that value is empty, use the domain in the recipient
       address.   Specify  "default_filter_nexthop  = $myhostname" for compatibility with Postfix
       version 2.6 and earlier, or specify  an	explicit  next-hop  destination  with  each  con-
       tent_filter value or FILTER action.

       This feature is available in Postfix 2.7 and later.

default_minimum_delivery_slots (default: 3)
       How  many  recipients  a  message must have in order to invoke the Postfix queue manager's
       scheduling algorithm at all.  Messages which would never accumulate  at	least  this  many
       delivery slots (subject to slot cost parameter as well) are never preempted.

       Use  transport_minimum_delivery_slots  to  specify  a  transport-specific  override, where
       transport is the master.cf name of the message delivery transport.

default_privs (default: nobody)
       The default rights used by the local(8) delivery agent for delivery to  external  file  or
       command.  These rights are used when delivery is requested from an aliases(5) file that is
       owned by root, or when delivery is done on behalf of root. DO  NOT  SPECIFY  A  PRIVILEGED
       USER OR THE POSTFIX OWNER.

default_process_limit (default: 100)
       The  default  maximal number of Postfix child processes that provide a given service. This
       limit can be overruled for specific services in the master.cf file.

default_rbl_reply (default: see postconf -d output)
       The default Postfix SMTP server response template for a request that  is  rejected  by  an
       RBL-based  restriction. This template can be overruled by specific entries in the optional
       rbl_reply_maps lookup table.

       This feature is available in Postfix 2.0 and later.

       The template is subject to exactly one level of $name substitution:

       $client
	      The client hostname and IP address, formatted as name[address].

       $client_address
	      The client IP address.

       $client_name
	      The client hostname  or  "unknown".  See	reject_unknown_client_hostname	for  more
	      details.

       $reverse_client_name
	      The    client    hostname   from	 address->name	 lookup,   or	"unknown".    See
	      reject_unknown_reverse_client_hostname for more details.

       $helo_name
	      The hostname given in HELO or EHLO command or empty string.

       $rbl_class
	      The blacklisted entity type: Client host, Helo command, Sender address, or  Recipi-
	      ent address.

       $rbl_code
	      The  numerical  SMTP response code, as specified with the maps_rbl_reject_code con-
	      figuration parameter. Note: The numerical SMTP response code is required, and  must
	      appear  at the start of the reply. With Postfix version 2.3 and later this informa-
	      tion may be followed by an RFC 3463 enhanced status code.

       $rbl_domain
	      The RBL domain where $rbl_what is blacklisted.

       $rbl_reason
	      The reason why $rbl_what is blacklisted, or an empty string.

       $rbl_what
	      The entity that is blacklisted (an IP address, a hostname, a  domain  name,  or  an
	      email address whose domain was blacklisted).

       $recipient
	      The recipient address or <> in case of the null address.

       $recipient_domain
	      The recipient domain or empty string.

       $recipient_name
	      The recipient address localpart or <> in case of null address.

       $sender
	      The sender address or <> in case of the null address.

       $sender_domain
	      The sender domain or empty string.

       $sender_name
	      The sender address localpart or <> in case of the null address.

       ${name?text}
	      Expands to `text' if $name is not empty.

       ${name:text}
	      Expands to `text' if $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Note: when an enhanced status code is specified in an RBL reply template, it is subject to
       modification.  The following transformations are needed when the same RBL  reply  template
       is used for client, helo, sender, or recipient access restrictions.

       o      When rejecting a sender address, the Postfix SMTP server will transform a recipient
	      DSN status (e.g., 4.1.1-4.1.6) into the corresponding sender DSN status,	and  vice
	      versa.

       o      When  rejecting  non-address  information (such as the HELO command argument or the
	      client hostname/address), the Postfix SMTP server will transform a sender or recip-
	      ient DSN status into a generic non-address DSN status (e.g., 4.0.0).

default_recipient_limit (default: 20000)
       The default per-transport upper limit on the number of in-memory recipients.  These limits
       take priority over the global qmgr_message_recipient_limit  after  the  message	has  been
       assigned  to  the  respective  transports.   See  also  default_extra_recipient_limit  and
       qmgr_message_recipient_minimum.

       Use transport_recipient_limit to specify a transport-specific override, where transport is
       the master.cf name of the message delivery transport.

default_recipient_refill_delay (default: 5s)
       The  default per-transport maximum delay between recipients refills.  When not all message
       recipients fit into the memory at once, keep loading more of them at least once every this
       many seconds.  This is used to make sure the recipients are refilled in timely manner even
       when $default_recipient_refill_limit is too high for too slow deliveries.

       Use transport_recipient_refill_delay  to  specify  a  transport-specific  override,  where
       transport is the master.cf name of the message delivery transport.

       This feature is available in Postfix 2.4 and later.

default_recipient_refill_limit (default: 100)
       The  default  per-transport  limit on the number of recipients refilled at once.  When not
       all message recipients fit into the memory at once, keep loading more of them  in  batches
       of  at  least  this  many  at a time.  See also $default_recipient_refill_delay, which may
       result in recipient batches lower than this when this limit  is	too  high  for	too  slow
       deliveries.

       Use  transport_recipient_refill_limit  to  specify  a  transport-specific  override, where
       transport is the master.cf name of the message delivery transport.

       This feature is available in Postfix 2.4 and later.

default_transport (default: smtp)
       The default mail delivery transport and next-hop destination for destinations that do  not
       match  $mydestination,  $inet_interfaces, $proxy_interfaces, $virtual_alias_domains, $vir-
       tual_mailbox_domains, or $relay_domains.  This  information  can  be  overruled	with  the
       sender_dependent_default_transport_maps parameter and with the transport(5) table.

       In  order  of  decreasing precedence, the nexthop destination is taken from $sender_depen-
       dent_default_transport_maps, $default_transport, $sender_dependent_relayhost_maps, $relay-
       host, or from the recipient domain.

       Specify	a  string  of  the  form transport:nexthop, where transport is the name of a mail
       delivery transport defined in master.cf.  The :nexthop destination is optional; its syntax
       is documented in the manual page of the corresponding delivery agent.

       Example:

       default_transport = uucp:relayhostname

default_verp_delimiters (default: +=)
       The  two default VERP delimiter characters. These are used when no explicit delimiters are
       specified with the SMTP XVERP command or with the "sendmail -V" command-line option. Spec-
       ify characters that are allowed by the verp_delimiter_filter setting.

       This feature is available in Postfix 1.1 and later.

defer_code (default: 450)
       The  numerical  Postfix	SMTP  server  response	code when a remote SMTP client request is
       rejected by the "defer" restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

defer_service_name (default: defer)
       The name of the defer service. This service is implemented by  the  bounce(8)  daemon  and
       maintains a record of failed delivery attempts and generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

defer_transports (default: empty)
       The  names  of  message	delivery  transports  that should not deliver mail unless someone
       issues "sendmail -q" or equivalent. Specify zero or more names of mail delivery transports
       names that appear in the first field of master.cf.

       Example:

       defer_transports = smtp

delay_logging_resolution_limit (default: 2)
       The maximal number of digits after the decimal point when logging sub-second delay values.
       Specify a number in the range 0..6.

       Large delay values are rounded off to an integral number seconds; delay values  below  the
       delay_logging_resolution_limit  are  logged as "0", and small delay values are logged with
       at most two-digit precision.

       The format of the "delays=a/b/c/d" logging is as follows:

       o      a = time from message arrival to last active queue entry

       o      b = time from last active queue entry to connection setup

       o      c = time in connection setup, including DNS, EHLO and STARTTLS

       o      d = time in message transmission

       This feature is available in Postfix 2.3 and later.

delay_notice_recipient (default: postmaster)
       The recipient of postmaster notifications with the message headers of mail that cannot  be
       delivered within $delay_warning_time time units.

       See also: delay_warning_time, notify_classes.

delay_warning_time (default: 0h)
       The  time  after  which	the sender receives a copy of the message headers of mail that is
       still queued.

       To enable this feature, specify a non-zero time value (an integral value plus an  optional
       one-letter suffix that specifies the time unit).

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is h (hours).

       See also: delay_notice_recipient, notify_classes.

deliver_lock_attempts (default: 20)
       The maximal number of attempts to acquire an exclusive lock on a mailbox file or bounce(8)
       logfile.

deliver_lock_delay (default: 1s)
       The time between attempts to acquire an exclusive lock on a mailbox file or bounce(8) log-
       file.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

destination_concurrency_feedback_debug (default: no)
       Make the queue manager's feedback algorithm verbose for performance analysis purposes.

       This feature is available in Postfix 2.5 and later.

detect_8bit_encoding_header (default: yes)
       Automatically  detect  8BITMIME body content by looking at Content-Transfer-Encoding: mes-
       sage headers; historically, this behavior was hard-coded to be "always on".

       This feature is available in Postfix 2.5 and later.

disable_dns_lookups (default: no)
       Disable DNS lookups in the Postfix SMTP and LMTP clients. When disabled, hosts are  looked
       up with the getaddrinfo() system library routine which normally also looks in /etc/hosts.

       DNS lookups are enabled by default.

disable_mime_input_processing (default: no)
       Turn  off  MIME	processing  while receiving mail. This means that no special treatment is
       given to Content-Type: message headers, and that all text after the initial message  head-
       ers is considered to be part of the message body.

       This feature is available in Postfix 2.0 and later.

       Mime  input  processing	is  enabled  by default, and is needed in order to recognize MIME
       headers in message content.

disable_mime_output_conversion (default: no)
       Disable the conversion of 8BITMIME format to  7BIT  format.   Mime  output  conversion  is
       needed when the destination does not advertise 8BITMIME support.

       This feature is available in Postfix 2.0 and later.

disable_verp_bounces (default: no)
       Disable sending one bounce report per recipient.

       The default, one per recipient, is what ezmlm needs.

       This feature is available in Postfix 1.1 and later.

disable_vrfy_command (default: no)
       Disable the SMTP VRFY command. This stops some techniques used to harvest email addresses.

       Example:

       disable_vrfy_command = no

dnsblog_reply_delay (default: 0s)
       A debugging aid to artificially delay DNS responses.

       This feature is available in Postfix 2.8.

dnsblog_service_name (default: dnsblog)
       The  name  of  the  dnsblog(8)  service	entry  in  master.cf.  This  service performs DNS
       white/blacklist lookups.

       This feature is available in Postfix 2.8 and later.

dont_remove (default: 0)
       Don't remove queue files and save them to the "saved" mail queue.   This  is  a	debugging
       aid.   To  inspect  the	envelope information and content of a Postfix queue file, use the
       postcat(1) command.

double_bounce_sender (default: double-bounce)
       The sender address of postmaster notifications that are generated by the mail system.  All
       mail to this address is silently discarded, in order to terminate mail bounce loops.

duplicate_filter_limit (default: 1000)
       The  maximal number of addresses remembered by the address duplicate filter for aliases(5)
       or virtual(5) alias expansion, or for showq(8) queue displays.

empty_address_default_transport_maps_lookup_key (default: <>)
       The sender_dependent_default_transport_maps search string that will be used instead of the
       null sender address.

       This feature is available in Postfix 2.7 and later.

empty_address_recipient (default: MAILER-DAEMON)
       The  recipient  of  mail  addressed  to	the  null  address.  Postfix does not accept such
       addresses in SMTP commands, but they may still be created locally as the result of config-
       uration or software error.

empty_address_relayhost_maps_lookup_key (default: <>)
       The  sender_dependent_relayhost_maps  search  string that will be used instead of the null
       sender address.

       This feature is available in Postfix 2.5 and later. With earlier  versions,  sender_depen-
       dent_relayhost_maps lookups were skipped for the null sender address.

enable_errors_to (default: no)
       Report mail delivery errors to the address specified with the non-standard Errors-To: mes-
       sage header, instead of the envelope sender address (this feature is removed with  Postfix
       version	2.2,  is  turned off by default with Postfix version 2.1, and is always turned on
       with older Postfix versions).

enable_long_queue_ids (default: no)
       Enable long, non-repeating, queue IDs (queue file names).  The  benefit	of  non-repeating
       names  is  simpler  logfile  analysis  and easier queue migration (there is no need to run
       "postsuper" to change queue file names that don't match their message file inode number).

       Note: see below for how to prepare long queue file names for migration to Postfix <= 2.8.

       Changing the parameter value to "yes" has the following effects:

       o      Existing queue file names are not affected.

       o      New queue files are created with names such as 3Pt2mN2VXxznjll.  These are  encoded
	      in a 52-character alphabet that contains digits (0-9), upper-case letters (B-Z) and
	      lower-case letters (b-z). For safety reasons the vowels (AEIOUaeiou)  are  excluded
	      from  the  alphabet.  The name format is: 6 or more characters for the time in sec-
	      onds, 4 characters for the time in microseconds, the 'z'; the remainder is the file
	      inode number encoded in the first 51 characters of the 52-character alphabet.

       o      New messages have a Message-ID header with queueID@myhostname.

       o      The  mailq (postqueue -p) output has a wider Queue ID column.  The number of white-
	      space-separated fields is not changed.

       o      The hash_queue_depth algorithm uses the first characters of the queue file creation
	      time  in	microseconds, after conversion into hexadecimal representation. This pro-
	      duces the same queue hashing behavior as if the queue file name  was  created  with
	      "enable_long_queue_ids = no".

       Changing the parameter value to "no" has the following effects:

       o      Existing	long queue file names are renamed to the short form (while running "post-
	      fix reload" or "postsuper").

       o      New queue files are created with names  such  as	C3CD21F3E90  from  a  hexadecimal
	      alphabet	that  contains digits (0-9) and upper-case letters (A-F). The name format
	      is: 5 characters for the time in microseconds; the remainder is the file inode num-
	      ber.

       o      New messages have a Message-ID header with YYYYMMDDHHMMSS.queueid@myhostname, where
	      YYYYMMDDHHMMSS are the year, month, day, hour, minute and second.

       o      The mailq (postqueue -p) output has the same format as with Postfix <= 2.8.

       o      The hash_queue_depth algorithm uses the first characters of the  queue  file  name,
	      with the hexadecimal representation of the file creation time in microseconds.

       Before  migration  to  Postfix <= 2.8, the following commands are required to convert long
       queue file names into short names:

       # postfix stop
       # postconf enable_long_queue_ids=no
       # postsuper

       Repeat the postsuper command until it reports no more queue file name changes.

       This feature is available in Postfix 2.9 and later.

enable_original_recipient (default: yes)
       Enable support for the X-Original-To message header. This  header  is  needed  for  multi-
       recipient mailboxes.

       When this parameter is set to yes, the cleanup(8) daemon performs duplicate elimination on
       distinct pairs of (original recipient, rewritten recipient), and generates non-empty orig-
       inal recipient queue file records.

       When  this parameter is set to no, the cleanup(8) daemon performs duplicate elimination on
       the rewritten recipient address only, and generates empty original  recipient  queue  file
       records.

       This  feature is available in Postfix 2.1 and later. With Postfix version 2.0, support for
       the X-Original-To message header is always turned on. Postfix versions before 2.0 have  no
       support for the X-Original-To message header.

error_notice_recipient (default: postmaster)
       The  recipient of postmaster notifications about mail delivery problems that are caused by
       policy, resource, software or protocol errors.  These notifications are enabled	with  the
       notify_classes parameter.

error_service_name (default: error)
       The  name of the error(8) pseudo delivery agent. This service always returns mail as unde-
       liverable.

       This feature is available in Postfix 2.0 and later.

execution_directory_expansion_filter (default: see postconf -d output)
       Restrict the characters that the local(8) delivery agent allows	in  $name  expansions  of
       $command_execution_directory.   Characters  outside the allowed set are replaced by under-
       scores.

       This feature is available in Postfix 2.2 and later.

expand_owner_alias (default: no)
       When delivering to an alias "aliasname" that has an "owner-aliasname" companion alias, set
       the  envelope  sender  address  to the expansion of the "owner-aliasname" alias. Normally,
       Postfix sets the envelope sender address to the name of the "owner-aliasname" alias.

export_environment (default: see postconf -d output)
       The list of environment variables that a Postfix process will export to	non-Postfix  pro-
       cesses. The TZ variable is needed for sane time keeping on System-V-ish systems.

       Specify	a  list  of  names and/or name=value pairs, separated by whitespace or comma. The
       name=value form is supported with Postfix version 2.1 and later.

       Example:

       export_environment = TZ PATH=/bin:/usr/bin

extract_recipient_limit (default: 10240)
       The maximal number of recipient addresses that Postfix will extract from  message  headers
       when mail is submitted with "sendmail -t".

       This feature was removed in Postfix version 2.1.

fallback_relay (default: empty)
       Optional  list  of  relay  hosts  for  SMTP  destinations  that can't be found or that are
       unreachable. With Postfix 2.3 this parameter is renamed to smtp_fallback_relay.

       By default, mail is returned to the sender when a destination is not found,  and  delivery
       is deferred when a destination is unreachable.

       The  fallback  relays  must  be	SMTP  destinations.  Specify  a  domain, host, host:port,
       [host]:port, [address] or [address]:port; the form [host] turns off MX  lookups.   If  you
       specify multiple SMTP destinations, Postfix will try them in the specified order.

       Note:  before  Postfix 2.2, do not use the fallback_relay feature when relaying mail for a
       backup or primary MX domain. Mail would loop between the Postfix MX  host  and  the  fall-
       back_relay host when the final destination is unavailable.

       o      In main.cf specify "relay_transport = relay",

       o      In  master.cf  specify  "-o fallback_relay =" (i.e., empty) at the end of the relay
	      entry.

       o      In transport maps, specify "relay:nexthop..."  as the right-hand side for backup or
	      primary MX domain entries.

       Postfix	version  2.2  and  later will not use the fallback_relay feature for destinations
       that it is MX host for.

fallback_transport (default: empty)
       Optional message delivery transport that the local(8) delivery agent should use for  names
       that are not found in the aliases(5) or UNIX password database.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,	  mailbox_transport,	mailbox_command_maps,	 mailbox_command,
       home_mailbox,   mail_spool_directory,   fallback_transport_maps,   fallback_transport  and
       luser_relay.

fallback_transport_maps (default: empty)
       Optional lookup tables with per-recipient message delivery transports for recipients  that
       the local(8) delivery agent could not find in the aliases(5) or UNIX password database.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,	  mailbox_transport,	mailbox_command_maps,	 mailbox_command,
       home_mailbox,   mail_spool_directory,   fallback_transport_maps,   fallback_transport  and
       luser_relay.

       For safety reasons, this feature does not allow $number substitutions in  regular  expres-
       sion maps.

       This feature is available in Postfix 2.3 and later.

fast_flush_domains (default: $relay_domains)
       Optional  list  of  destinations  that are eligible for per-destination logfiles with mail
       that is queued to those destinations.

       By default, Postfix maintains "fast flush" logfiles only for destinations that the Postfix
       SMTP  server  is  willing  to  relay  to  (i.e.	the  default  is:  "fast_flush_domains	=
       $relay_domains"; see the relay_domains parameter in the postconf(5) manual).

       Specify a list of hosts or domains, "/file/name" patterns or "type:table"  lookup  tables,
       separated by commas and/or whitespace.  Continue long lines by starting the next line with
       whitespace. A "/file/name" pattern is replaced by its contents; a "type:table" lookup  ta-
       ble is matched when the domain or its parent domain appears as lookup key.

       Specify "fast_flush_domains =" (i.e., empty) to disable the feature altogether.

fast_flush_purge_time (default: 7d)
       The time after which an empty per-destination "fast flush" logfile is deleted.

       You  can  specify the time as a number, or as a number followed by a letter that indicates
       the time unit: s=seconds, m=minutes, h=hours, d=days, w=weeks.  The default time  unit  is
       days.

fast_flush_refresh_time (default: 12h)
       The  time after which a non-empty but unread per-destination "fast flush" logfile needs to
       be refreshed.  The contents of a logfile are refreshed by requesting delivery of all  mes-
       sages listed in the logfile.

       You  can  specify the time as a number, or as a number followed by a letter that indicates
       the time unit: s=seconds, m=minutes, h=hours, d=days, w=weeks.  The default time  unit  is
       hours.

fault_injection_code (default: 0)
       Force  specific	internal tests to fail, to test the handling of errors that are difficult
       to reproduce otherwise.

flush_service_name (default: flush)
       The name of the flush(8) service. This service maintains per-destination logfiles with the
       queue file names of mail that is queued for those destinations.

       This feature is available in Postfix 2.0 and later.

fork_attempts (default: 5)
       The maximal number of attempts to fork() a child process.

fork_delay (default: 1s)
       The delay between attempts to fork() a child process.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

forward_expansion_filter (default: see postconf -d output)
       Restrict the characters that the local(8) delivery agent allows	in  $name  expansions  of
       $forward_path.  Characters outside the allowed set are replaced by underscores.

forward_path (default: see postconf -d output)
       The  local(8)  delivery	agent search list for finding a .forward file with user-specified
       delivery methods. The first file that is found is used.

       The following $name expansions are done on forward_path before the  search  actually  hap-
       pens.  The  result of $name expansion is filtered with the character set that is specified
       with the forward_expansion_filter parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
	      The full recipient address.

       $extension
	      The optional recipient address extension.

       $domain
	      The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
	      The system-wide recipient address extension delimiter.

       ${name?value}
	      Expands to value when $name is non-empty.

       ${name:value}
	      Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Examples:

       forward_path = /var/forward/$user
       forward_path =
	   /var/forward/$user/.forward$recipient_delimiter$extension,
	   /var/forward/$user/.forward

frozen_delivered_to (default: yes)
       Update the local(8) delivery agent's idea of the Delivered-To: address (see prepend_deliv-
       ered_header)  only  once, at the start of a delivery attempt; do not update the Delivered-
       To: address while expanding aliases or .forward files.

       This feature is available in Postfix 2.3 and  later.  With  older  Postfix  releases,  the
       behavior  is  as  if  this parameter is set to "no". The old setting can be expensive with
       deeply nested aliases or .forward files. When an alias or .forward file changes the Deliv-
       ered-To: address, it ties up one queue file and one cleanup process instance while mail is
       being forwarded.

hash_queue_depth (default: 1)
       The number of subdirectory levels for queue directories listed with  the  hash_queue_names
       parameter. Queue hashing is implemented by creating one or more levels of directories with
       one-character names.  Originally, these directory names were equal to the first characters
       of  the	queue file name, with the hexadecimal representation of the file creation time in
       microseconds.

       With long queue file names, queue hashing produces the same results as with  short  names.
       The  file  creation  time  in  microseconds  is converted into hexadecimal form before the
       result is used for queue hashing.  The base 16 encoding gives finer control over the  num-
       ber of subdirectories than is possible with the base 52 encoding of long queue file names.

       After  changing	the  hash_queue_names  or hash_queue_depth parameter, execute the command
       "postfix reload".

hash_queue_names (default: deferred, defer)
       The names of queue directories that are split across multiple subdirectory levels.

       Before Postfix version 2.2, the default list of hashed queues  was  significantly  larger.
       Claims  about  improvements in file system technology suggest that hashing of the incoming
       and active queues is no longer needed. Fewer hashed directories speed up the  time  needed
       to restart Postfix.

       After  changing	the  hash_queue_names  or hash_queue_depth parameter, execute the command
       "postfix reload".

header_address_token_limit (default: 10240)
       The maximal number of address tokens are allowed in an address message header. Information
       that exceeds the limit is discarded.  The limit is enforced by the cleanup(8) server.

header_checks (default: empty)
       Optional  lookup  tables  for  content  inspection of primary non-MIME message headers, as
       specified in the header_checks(5) manual page.

header_size_limit (default: 102400)
       The maximal amount of memory in bytes for storing  a  message  header.	If  a  header  is
       larger, the excess is discarded.  The limit is enforced by the cleanup(8) server.

helpful_warnings (default: yes)
       Log warnings about problematic configuration settings, and provide helpful suggestions.

       This feature is available in Postfix 2.0 and later.

home_mailbox (default: empty)
       Optional pathname of a mailbox file relative to a local(8) user's home directory.

       Specify a pathname ending in "/" for qmail-style delivery.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,	  mailbox_transport,	mailbox_command_maps,	 mailbox_command,
       home_mailbox,   mail_spool_directory,   fallback_transport_maps,   fallback_transport  and
       luser_relay.

       Examples:

       home_mailbox = Mailbox
       home_mailbox = Maildir/

hopcount_limit (default: 50)
       The maximal number of Received:	message headers that is allowed in  the  primary  message
       headers. A message that exceeds the limit is bounced, in order to stop a mailer loop.

html_directory (default: see postconf -d output)
       The location of Postfix HTML files that describe how to build, configure or operate a spe-
       cific Postfix subsystem or feature.

ignore_mx_lookup_error (default: no)
       Ignore DNS MX lookups that produce no response.	 By  default,  the  Postfix  SMTP  client
       defers  delivery  and tries again after some delay.  This behavior is required by the SMTP
       standard.

       Specify "ignore_mx_lookup_error = yes" to force a DNS A record lookup instead.  This  vio-
       lates the SMTP standard and can result in mis-delivery of mail.

import_environment (default: see postconf -d output)
       The  list  of environment parameters that a Postfix process will import from a non-Postfix
       parent process. Examples of relevant parameters:

       TZ     Needed for sane time keeping on most System-V-ish systems.

       DISPLAY
	      Needed for debugging Postfix daemons with an X-windows debugger.

       XAUTHORITY
	      Needed for debugging Postfix daemons with an X-windows debugger.

       MAIL_CONFIG
	      Needed to make "postfix -c" work.

       Specify a list of names and/or name=value pairs, separated by  whitespace  or  comma.  The
       name=value form is supported with Postfix version 2.1 and later.

in_flow_delay (default: 1s)
       Time  to  pause	before accepting a new message, when the message arrival rate exceeds the
       message delivery rate. This feature is turned on by default (it's disabled on SCO UNIX due
       to an SCO bug).

       With  the  default  100 Postfix SMTP server process limit, "in_flow_delay = 1s" limits the
       mail inflow to 100 messages per second above the number of messages delivered per second.

       Specify 0 to disable the feature. Valid delays are 0..10.

inet_interfaces (default: all)
       The network interface addresses that this mail system receives mail on. Specify	"all"  to
       receive	mail  on all network interfaces (default), and "loopback-only" to receive mail on
       loopback network interfaces only (Postfix version 2.2 and later).  The parameter also con-
       trols delivery of mail to user@[ip.address].

       Note 1: you need to stop and start Postfix when this parameter changes.

       Note 2: address information may be enclosed inside [], but this form is not required here.

       When  inet_interfaces  specifies  just one IPv4 and/or IPv6 address that is not a loopback
       address, the Postfix SMTP client will use this address as the IP source address	for  out-
       bound mail. Support for IPv6 is available in Postfix version 2.2 and later.

       On  a  multi-homed  firewall with separate Postfix instances listening on the "inside" and
       "outside" interfaces, this can prevent each instance from being able to reach remote  SMTP
       servers	on  the "other side" of the firewall. Setting smtp_bind_address to 0.0.0.0 avoids
       the potential problem for IPv4, and setting smtp_bind_address6 to ::  solves  the  problem
       for IPv6.

       A  better  solution  for  multi-homed firewalls is to leave inet_interfaces at the default
       value and instead use explicit IP addresses in  the  master.cf  SMTP  server  definitions.
       This preserves the Postfix SMTP client's loop detection, by ensuring that each side of the
       firewall knows that the other IP address is still the same host. Setting  $inet_interfaces
       to  a  single IPv4 and/or IPV6 address is primarily useful with virtual hosting of domains
       on secondary IP addresses, when each IP address serves a different domain (and has a  dif-
       ferent $myhostname setting).

       See also the proxy_interfaces parameter, for network addresses that are forwarded to Post-
       fix by way of a proxy or address translator.

       Examples:

       inet_interfaces = all (DEFAULT)
       inet_interfaces = loopback-only (Postfix version 2.2 and later)
       inet_interfaces = 127.0.0.1
       inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
       inet_interfaces = 192.168.1.2, 127.0.0.1

inet_protocols (default: all)
       The Internet protocols Postfix will attempt to use when making or  accepting  connections.
       Specify one or more of "ipv4" or "ipv6", separated by whitespace or commas. The form "all"
       is equivalent to "ipv4, ipv6" or "ipv4", depending on whether the operating system  imple-
       ments IPv6.

       With Postfix 2.8 and earlier the default is "ipv4". For backwards compatibility with these
       releases, the Postfix 2.9 and later upgrade procedure appends an explicit  "inet_protocols
       =  ipv4"  setting to main.cf when no explicit setting is present. This compatibility work-
       around will be phased out as IPv6 deployment becomes more common.

       This feature is available in Postfix 2.2 and later.

       Note: you MUST stop and start Postfix after changing this parameter.

       On systems that pre-date IPV6_V6ONLY support (RFC 3493), an IPv6 server will  also  accept
       IPv4 connections, even when IPv4 is turned off with the inet_protocols parameter.  On sys-
       tems with IPV6_V6ONLY support, Postfix will use separate server sockets for IPv6 and IPv4,
       and each will accept only connections for the corresponding protocol.

       When  IPv4  support  is enabled via the inet_protocols parameter, Postfix will look up DNS
       type A records, and will convert IPv4-in-IPv6  client  IP  addresses  (::ffff:1.2.3.4)  to
       their  original	IPv4  form  (1.2.3.4).	 The  latter  is  needed  on  hosts that pre-date
       IPV6_V6ONLY support (RFC 3493).

       When IPv6 support is enabled via the inet_protocols parameter, Postfix will  do	DNS  type
       AAAA record lookups.

       When  both IPv4 and IPv6 support are enabled, the Postfix SMTP client will attempt to con-
       nect via IPv6 before attempting to use IPv4.

       Examples:

       inet_protocols = ipv4
       inet_protocols = all (DEFAULT)
       inet_protocols = ipv6
       inet_protocols = ipv4, ipv6

initial_destination_concurrency (default: 5)
       The initial per-destination concurrency level for parallel delivery to the  same  destina-
       tion.   With  per-destination recipient limit > 1, a destination is a domain, otherwise it
       is a recipient.

       Use transport_initial_destination_concurrency to specify  a  transport-specific	override,
       where  transport  is the master.cf name of the message delivery transport (Postfix 2.5 and
       later).

       Warning: with concurrency of 1, one bad message can be enough to block all mail to a site.

internal_mail_filter_classes (default: empty)
       What categories of Postfix-generated mail are subject to before-queue  content  inspection
       by  non_smtpd_milters, header_checks and body_checks.  Specify zero or more of the follow-
       ing, separated by whitespace or comma.

       bounce Inspect the content of delivery status notifications.

       notify Inspect the content of postmaster notifications by the smtp(8)  and  smtpd(8)  pro-
	      cesses.

       NOTE: It's generally not safe to enable content inspection of Postfix-generated email mes-
       sages. The user is warned.

       This feature is available in Postfix 2.3 and later.

invalid_hostname_reject_code (default: 501)
       The numerical Postfix SMTP server response code when  the  client  HELO	or  EHLO  command
       parameter is rejected by the reject_invalid_helo_hostname restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

ipc_idle (default: version dependent)
       The  time after which a client closes an idle internal communication channel.  The purpose
       is to allow Postfix daemon processes to terminate voluntarily after they become idle. This
       is used, for example, by the Postfix address resolving and rewriting clients.

       With Postfix 2.4 the default value was reduced from 100s to 5s.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

ipc_timeout (default: 3600s)
       The time limit for sending or receiving information over an internal  communication  chan-
       nel.   The  purpose  is to break out of deadlock situations. If the time limit is exceeded
       the software aborts with a fatal error.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

ipc_ttl (default: 1000s)
       The  time  after which a client closes an active internal communication channel.  The pur-
       pose is to allow Postfix daemon processes to terminate voluntarily  after  reaching  their
       client  limit.	This is used, for example, by the Postfix address resolving and rewriting
       clients.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

line_length_limit (default: 2048)
       Upon  input,  long lines are chopped up into pieces of at most this length; upon delivery,
       long lines are reconstructed.

lmtp_address_preference (default: ipv6)
       The LMTP-specific version of the  smtp_address_preference  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_assume_final (default: no)
       When  a remote LMTP server announces no DSN support, assume that the server performs final
       delivery, and send "delivered" delivery status notifications  instead  of  "relayed".  The
       default setting is backwards compatible to avoid the infinitesimal possibility of breaking
       existing LMTP-based content filters.

lmtp_bind_address (default: empty)
       The LMTP-specific version of the smtp_bind_address configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_bind_address6 (default: empty)
       The  LMTP-specific  version  of the smtp_bind_address6 configuration parameter.	See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_body_checks (default: empty)
       The LMTP-specific version of the smtp_body_checks configuration parameter. See  there  for
       details.

       This feature is available in Postfix 2.5 and later.

lmtp_cache_connection (default: yes)
       Keep  Postfix  LMTP  client  connections  open  for up to $max_idle seconds. When the LMTP
       client receives a request for the same connection the connection is reused.

       This parameter is available in Postfix version 2.2 and earlier.	With Postfix version  2.3
       and  later,  see  lmtp_connection_cache_on_demand,  lmtp_connection_cache_destinations, or
       lmtp_connection_reuse_time_limit.

       The effectiveness of cached connections will be determined by the number  of  remote  LMTP
       servers	in  use,  and the concurrency limit specified for the Postfix LMTP client. Cached
       connections are closed under any of the following conditions:

       o      The Postfix LMTP client idle time limit is reached.  This limit is  specified  with
	      the Postfix max_idle configuration parameter.

       o      A delivery request specifies a different destination than the one currently cached.

       o      The per-process limit on the number of delivery requests is reached.  This limit is
	      specified with the Postfix max_use configuration parameter.

       o      Upon the onset of another delivery request, the remote LMTP server associated  with
	      the current session does not respond to the RSET command.

       Most  of  these	limitations  have been with the Postfix a connection cache that is shared
       among multiple LMTP client programs.

lmtp_cname_overrides_servername (default: yes)
       The LMTP-specific version of the smtp_cname_overrides_servername configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connect_timeout (default: 0s)
       The Postfix LMTP client time limit for completing a TCP connection, or zero (use the oper-
       ating system built-in time limit).  When no connection can be made  within  the	deadline,
       the LMTP client tries the next address on the mail exchanger list.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

       Example:

       lmtp_connect_timeout = 30s

lmtp_connection_cache_destinations (default: empty)
       The LMTP-specific version of the smtp_connection_cache_destinations configuration  parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_on_demand (default: yes)
       The  LMTP-specific version of the smtp_connection_cache_on_demand configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_time_limit (default: 2s)
       The LMTP-specific version of the smtp_connection_cache_time_limit configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_reuse_time_limit (default: 300s)
       The LMTP-specific version of the smtp_connection_reuse_time_limit configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_data_done_timeout (default: 600s)
       The Postfix LMTP client time limit for sending the LMTP ".", and for receiving the  remote
       LMTP  server  response.	 When  no  response is received within the deadline, a warning is
       logged that the mail may be delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_data_init_timeout (default: 120s)
       The  Postfix  LMTP  client time limit for sending the LMTP DATA command, and for receiving
       the remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_data_xfer_timeout (default: 180s)
       The Postfix LMTP client time limit for sending the LMTP message content.  When the connec-
       tion stalls for more than $lmtp_data_xfer_timeout the LMTP client terminates the transfer.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_defer_if_no_mx_address_found (default: no)
       The  LMTP-specific  version of the smtp_defer_if_no_mx_address_found configuration parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_destination_concurrency_limit (default: $default_destination_concurrency_limit)
       The maximal number of parallel deliveries to the same destination  via  the  lmtp  message
       delivery  transport.  This  limit  is  enforced by the queue manager. The message delivery
       transport name is the first field in the entry in the master.cf file.

lmtp_destination_recipient_limit (default: $default_destination_recipient_limit)
       The maximal number of recipients per message for the lmtp message delivery transport. This
       limit  is  enforced by the queue manager. The message delivery transport name is the first
       field in the entry in the master.cf file.

       Setting this parameter to a value of 1 changes  the  meaning  of  lmtp_destination_concur-
       rency_limit from concurrency per domain into concurrency per recipient.

lmtp_discard_lhlo_keyword_address_maps (default: empty)
       Lookup  tables,	indexed by the remote LMTP server address, with case insensitive lists of
       LHLO keywords (pipelining, starttls, auth, etc.) that the Postfix LMTP client will  ignore
       in  the	LHLO  response	from  a  remote  LMTP  server. See lmtp_discard_lhlo_keywords for
       details. The table is not indexed by hostname for consistency with smtpd_discard_ehlo_key-
       word_address_maps.

       This feature is available in Postfix 2.3 and later.

lmtp_discard_lhlo_keywords (default: empty)
       A case insensitive list of LHLO keywords (pipelining, starttls, auth, etc.) that the Post-
       fix LMTP client will ignore in the LHLO response from a remote LMTP server.

       This feature is available in Postfix 2.3 and later.

       Notes:

       o      Specify the silent-discard pseudo keyword to prevent this action from being logged.

       o      Use the lmtp_discard_lhlo_keyword_address_maps feature  to  discard  LHLO  keywords
	      selectively.

lmtp_dns_resolver_options (default: empty)
       The  LMTP-specific  version of the smtp_dns_resolver_options configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_enforce_tls (default: no)
       The LMTP-specific version of the smtp_enforce_tls configuration parameter.  See there  for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_generic_maps (default: empty)
       The LMTP-specific version of the smtp_generic_maps configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_header_checks (default: empty)
       The LMTP-specific version of the smtp_header_checks configuration parameter. See there for
       details.

       This feature is available in Postfix 2.5 and later.

lmtp_host_lookup (default: dns)
       The  LMTP-specific version of the smtp_host_lookup configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_name (default: $myhostname)
       The hostname to send in the LMTP LHLO command.

       The default value is the machine hostname.  Specify a hostname or [ip.add.re.ss].

       This information can be specified in the main.cf file for all LMTP clients, or it  can  be
       specified in the master.cf file for a specific client, for example:

	   /etc/postfix/master.cf:
	       mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_timeout (default: 300s)
       The  Postfix  LMTP  client  time limit for sending the LHLO command, and for receiving the
       initial remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_line_length_limit (default: 990)
       The  LMTP-specific  version  of	the  smtp_line_length_limit configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mail_timeout (default: 300s)
       The Postfix LMTP client time limit for sending the MAIL FROM command,  and  for	receiving
       the remote LMTP server response.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

lmtp_mime_header_checks (default: empty)
       The LMTP-specific version of  the  smtp_mime_header_checks  configuration  parameter.  See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_mx_address_limit (default: 5)
       The LMTP-specific version of the smtp_mx_address_limit configuration parameter.	See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mx_session_limit (default: 2)
       The LMTP-specific version of the smtp_mx_session_limit configuration parameter.	See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_nested_header_checks (default: empty)
       The  LMTP-specific  version  of the smtp_nested_header_checks configuration parameter. See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_per_record_deadline (default: no)
       The LMTP-specific version of the smtp_per_record_deadline  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.9 and later.

lmtp_pix_workaround_delay_time (default: 10s)
       The  LMTP-specific  version of the smtp_pix_workaround_delay_time configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workaround_maps (default: empty)
       The LMTP-specific version of the smtp_pix_workaround_maps  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_pix_workaround_threshold_time (default: 500s)
       The  LMTP-specific version of the smtp_pix_workaround_threshold_time configuration parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workarounds (default: empty)
       The LMTP-specific version of the smtp_pix_workaround configuration parameter.   See  there
       for details.

       This feature is available in Postfix 2.4 and later.

lmtp_quit_timeout (default: 300s)
       The  Postfix  LMTP  client  time limit for sending the QUIT command, and for receiving the
       remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_quote_rfc821_envelope (default: yes)
       The  LMTP-specific version of the smtp_quote_rfc821_envelope configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_randomize_addresses (default: yes)
       The LMTP-specific version of the smtp_randomize_addresses  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_rcpt_timeout (default: 300s)
       The  Postfix LMTP client time limit for sending the RCPT TO command, and for receiving the
       remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_reply_filter (default: empty)
       The LMTP-specific version of the smtp_reply_filter configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.7 and later.

lmtp_rset_timeout (default: 20s)
       The Postfix LMTP client time limit for sending the RSET command,  and  for  receiving  the
       remote  LMTP  server  response.	The LMTP client sends RSET in order to finish a recipient
       address probe, or to verify that a cached connection is still alive.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_sasl_auth_cache_name (default: empty)
       The  LMTP-specific  version of the smtp_sasl_auth_cache_name configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_cache_time (default: 90d)
       The LMTP-specific version of the smtp_sasl_auth_cache_time configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix LMTP client.

lmtp_sasl_auth_soft_bounce (default: yes)
       The  LMTP-specific version of the smtp_sasl_auth_soft_bounce configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_mechanism_filter (default: empty)
       The LMTP-specific version of the smtp_sasl_mechanism_filter configuration parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_password_maps (default: empty)
       Optional  Postfix  LMTP	client lookup tables with one username:password entry per host or
       domain.	If a remote host or domain has no username:password entry, then the Postfix  LMTP
       client will not attempt to authenticate to the remote host.

lmtp_sasl_path (default: empty)
       Implementation-specific information that is passed through to the SASL plug-in implementa-
       tion that is selected with lmtp_sasl_type.  Typically this specifies the name of a config-
       uration file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_security_options (default: noplaintext, noanonymous)
       SASL  security  options;  as  of Postfix 2.3 the list of available features depends on the
       SASL client implementation that is selected with lmtp_sasl_type.

       The following security features are defined for the cyrus client SASL implementation:

       noplaintext
	      Disallow authentication methods that use plaintext passwords.

       noactive
	      Disallow authentication  methods	that  are  vulnerable  to  non-dictionary  active
	      attacks.

       nodictionary
	      Disallow authentication methods that are vulnerable to passive dictionary attack.

       noanonymous
	      Disallow anonymous logins.

       Example:

       lmtp_sasl_security_options = noplaintext

lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options)
       The  LMTP-specific  version of the smtp_sasl_tls_security_options configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_tls_verified_security_options (default: $lmtp_sasl_tls_security_options)
       The LMTP-specific version  of  the  smtp_sasl_tls_verified_security_options  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_type (default: cyrus)
       The  SASL  plug-in  type  that the Postfix LMTP client should use for authentication.  The
       available types are listed with the "postconf -A" command.

       This feature is available in Postfix 2.3 and later.

lmtp_send_dummy_mail_auth (default: no)
       The LMTP-specific version of the smtp_send_dummy_mail_auth configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.9 and later.

lmtp_send_xforward_command (default: no)
       Send  an  XFORWARD  command  to	the remote LMTP server when the LMTP LHLO server response
       announces XFORWARD support.  This allows an lmtp(8) delivery agent, used for content  fil-
       ter  message injection, to forward the name, address, protocol and HELO name of the origi-
       nal client to the content filter and downstream queuing LMTP server.   Before  you  change
       the value to yes, it is best to make sure that your content filter supports this command.

       This feature is available in Postfix 2.1 and later.

lmtp_sender_dependent_authentication (default: no)
       The LMTP-specific version of the smtp_sender_dependent_authentication configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_5xx_greeting (default: yes)
       The LMTP-specific version of  the  smtp_skip_5xx_greeting  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_quit_response (default: no)
       Wait for the response to the LMTP QUIT command.

lmtp_starttls_timeout (default: 300s)
       The LMTP-specific version of the smtp_starttls_timeout configuration parameter.	See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tcp_port (default: 24)
       The default TCP port that the Postfix LMTP client connects to.

lmtp_tls_CAfile (default: empty)
       The LMTP-specific version of the smtp_tls_CAfile configuration parameter.  See  there  for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_CApath (default: empty)
       The  LMTP-specific  version of the smtp_tls_CApath configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_block_early_mail_reply (default: empty)
       The LMTP-specific version of the smtp_tls_block_early_mail_reply configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_tls_cert_file (default: empty)
       The  LMTP-specific  version  of the smtp_tls_cert_file configuration parameter.	See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_ciphers (default: export)
       The LMTP-specific version of the smtp_tls_ciphers configuration parameter. See  there  for
       details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_dcert_file (default: empty)
       The  LMTP-specific  version of the smtp_tls_dcert_file configuration parameter.	See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file)
       The LMTP-specific version of the smtp_tls_dkey_file configuration  parameter.   See  there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_eccert_file (default: empty)
       The  LMTP-specific version of the smtp_tls_eccert_file configuration parameter.	See there
       for details.

       This feature is available in Postfix 2.6 and later, when Postfix is  compiled  and  linked
       with OpenSSL 1.0.0 or later.

lmtp_tls_eckey_file (default: empty)
       The  LMTP-specific  version of the smtp_tls_eckey_file configuration parameter.	See there
       for details.

       This feature is available in Postfix 2.6 and later, when Postfix is  compiled  and  linked
       with OpenSSL 1.0.0 or later.

lmtp_tls_enforce_peername (default: yes)
       The  LMTP-specific  version of the smtp_tls_enforce_peername configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_exclude_ciphers (default: empty)
       The LMTP-specific version of the smtp_tls_exclude_ciphers  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_fingerprint_cert_match (default: empty)
       The  LMTP-specific version of the smtp_tls_fingerprint_cert_match configuration parameter.
       See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_fingerprint_digest (default: md5)
       The LMTP-specific version of the smtp_tls_fingerprint_digest configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_key_file (default: $lmtp_tls_cert_file)
       The LMTP-specific version of the smtp_tls_key_file configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_loglevel (default: 0)
       The LMTP-specific version of the smtp_tls_loglevel configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_ciphers (default: empty)
       The  LMTP-specific version of the smtp_tls_mandatory_ciphers configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_exclude_ciphers (default: empty)
       The LMTP-specific version of the smtp_tls_mandatory_exclude_ciphers configuration  parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_protocols (default: !SSLv2)
       The LMTP-specific version of the smtp_tls_mandatory_protocols configuration parameter. See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_note_starttls_offer (default: no)
       The LMTP-specific version of  the  smtp_tls_note_starttls_offer	configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_per_site (default: empty)
       The LMTP-specific version of the smtp_tls_per_site configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_policy_maps (default: empty)
       The LMTP-specific version of the smtp_tls_policy_maps configuration parameter.  See  there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_protocols (default: empty)
       The LMTP-specific version of the smtp_tls_protocols configuration parameter. See there for
       details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_scert_verifydepth (default: 9)
       The LMTP-specific version of the smtp_tls_scert_verifydepth configuration parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_secure_cert_match (default: nexthop)
       The  LMTP-specific  version of the smtp_tls_secure_cert_match configuration parameter. See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_security_level (default: empty)
       The LMTP-specific version of the  smtp_tls_security_level  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_database (default: empty)
       The  LMTP-specific version of the smtp_tls_session_cache_database configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_timeout (default: 3600s)
       The LMTP-specific version of the smtp_tls_session_cache_timeout	configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_verify_cert_match (default: hostname)
       The  LMTP-specific  version of the smtp_tls_verify_cert_match configuration parameter. See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_use_tls (default: no)
       The LMTP-specific version of the smtp_use_tls  configuration  parameter.   See  there  for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_xforward_timeout (default: 300s)
       The Postfix LMTP client time limit for sending the XFORWARD command, and for receiving the
       remote LMTP server response.

       In case of problems the client does NOT try the next address on the mail exchanger list.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

local_command_shell (default: empty)
       Optional  shell	program  for  local(8) delivery to non-Postfix command.  By default, non-
       Postfix commands are executed directly; commands are given to given to the  default  shell
       (typically,  /bin/sh)  only when they contain shell meta characters or shell built-in com-
       mands.

       "sendmail's restricted shell" (smrsh) is what most people will use in  order  to  restrict
       what programs can be run from e.g. .forward files (smrsh is part of the Sendmail distribu-
       tion).

       Note: when a shell program is specified, it is invoked even when the command  contains  no
       shell built-in commands or meta characters.

       Example:

       local_command_shell = /some/where/smrsh -c
       local_command_shell = /bin/bash -c

local_destination_concurrency_limit (default: 2)
       The  maximal  number  of  parallel deliveries via the local mail delivery transport to the
       same recipient (when "local_destination_recipient_limit = 1") or  the  maximal  number  of
       parallel  deliveries  to  the same local domain (when "local_destination_recipient_limit >
       1"). This limit is enforced by the queue manager. The message delivery transport  name  is
       the first field in the entry in the master.cf file.

       A  low limit of 2 is recommended, just in case someone has an expensive shell command in a
       .forward file or in an alias (e.g., a mailing list manager).  You don't want to	run  lots
       of those at the same time.

local_destination_recipient_limit (default: 1)
       The  maximal  number of recipients per message delivery via the local mail delivery trans-
       port. This limit is enforced by the queue manager. The message delivery transport name  is
       the first field in the entry in the master.cf file.

       Setting	this  parameter  to  a value > 1 changes the meaning of local_destination_concur-
       rency_limit from concurrency per recipient into concurrency per domain.

local_header_rewrite_clients (default: permit_inet_interfaces)
       Rewrite message header  addresses  in  mail  from  these  clients  and  update  incomplete
       addresses  with	the  domain  name in $myorigin or $mydomain; either don't rewrite message
       headers from other clients at all,  or  rewrite	message  headers  and  update  incomplete
       addresses with the domain specified in the remote_header_rewrite_domain parameter.

       See  the  append_at_myorigin  and append_dot_mydomain parameters for details of how domain
       names are appended to incomplete addresses.

       Specify a list of zero or more of the following:

       permit_inet_interfaces
	      Append the domain name in $myorigin or $mydomain when the client IP address matches
	      $inet_interfaces. This is enabled by default.

       permit_mynetworks
	      Append the domain name in $myorigin or $mydomain when the client IP address matches
	      any network or network address listed in $mynetworks. This setting will not prevent
	      remote mail header address rewriting when mail from a remote client is forwarded by
	      a neighboring system.

       permit_sasl_authenticated
	      Append the domain name in $myorigin or $mydomain when the  client  is  successfully
	      authenticated via the RFC 4954 (AUTH) protocol.

       permit_tls_clientcerts
	      Append  the  domain  name in $myorigin or $mydomain when the remote SMTP client TLS
	      certificate fingerprint or public key fingerprint (Postfix 2.9 and later) is listed
	      in  $relay_clientcerts.	The  fingerprint digest algorithm is configurable via the
	      smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to Postfix  version
	      2.5).

       permit_tls_all_clientcerts
	      Append  the  domain  name in $myorigin or $mydomain when the remote SMTP client TLS
	      certificate is successfully verified, regardless of whether it  is  listed  on  the
	      server, and regardless of the certifying authority.

       check_address_map type:table

       type:table
	      Append the domain name in $myorigin or $mydomain when the client IP address matches
	      the specified lookup table.  The lookup result is ignored, and no subnet lookup  is
	      done. This is suitable for, e.g., pop-before-smtp lookup tables.

       Examples:

       The Postfix < 2.2 backwards compatible setting: always rewrite message headers, and always
       append my own domain to incomplete header addresses.

	   local_header_rewrite_clients = static:all

       The purist (and default) setting: rewrite headers only in mail from Postfix  sendmail  and
       in SMTP mail from this machine.

	   local_header_rewrite_clients = permit_inet_interfaces

       The  intermediate  setting:  rewrite  header  addresses	and append $myorigin or $mydomain
       information only with mail from Postfix sendmail, from local clients, or  from  authorized
       SMTP clients.

       Note:  this setting will not prevent remote mail header address rewriting when mail from a
       remote client is forwarded by a neighboring system.

	   local_header_rewrite_clients = permit_mynetworks,
	       permit_sasl_authenticated permit_tls_clientcerts
	       check_address_map hash:/etc/postfix/pop-before-smtp

local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)
       Lookup tables with all names or addresses of local  recipients:	a  recipient  address  is
       local  when  its  domain  matches  $mydestination,  $inet_interfaces or $proxy_interfaces.
       Specify @domain as a wild-card for domains that do not have a valid recipient list.  Tech-
       nically, tables listed with $local_recipient_maps are used as lists: Postfix needs to know
       only if a lookup string is found or not, but it does not use the result from table lookup.

       If this parameter is non-empty (the default), then the Postfix  SMTP  server  will  reject
       mail for unknown local users.

       To  turn  off  local recipient checking in the Postfix SMTP server, specify "local_recipi-
       ent_maps =" (i.e. empty).

       The default setting assumes that you use the default  Postfix  local  delivery  agent  for
       local delivery. You need to update the local_recipient_maps setting if:

       o      You redefine the local delivery agent in master.cf.

       o      You redefine the "local_transport" setting in main.cf.

       o      You  use the "luser_relay", "mailbox_transport", or "fallback_transport" feature of
	      the Postfix local(8) delivery agent.

       Details are described in the LOCAL_RECIPIENT_README file.

       Beware: if the Postfix SMTP server runs chrooted, you need to access the passwd	file  via
       the proxymap(8) service, in order to overcome chroot access restrictions. The alternative,
       maintaining a copy of the system password file in the chroot jail is not practical.

       Examples:

       local_recipient_maps =

local_transport (default: local:$myhostname)
       The default mail delivery transport and next-hop destination for final delivery to domains
       listed with mydestination, and for [ipaddress] destinations that match $inet_interfaces or
       $proxy_interfaces.  This information can be overruled with the transport(5) table.

       By default, local mail is delivered to the transport called "local",  which  is	just  the
       name of a service that is defined the master.cf file.

       Specify	a  string  of  the  form transport:nexthop, where transport is the name of a mail
       delivery transport defined in master.cf.  The :nexthop destination is optional; its syntax
       is documented in the manual page of the corresponding delivery agent.

       Beware:	if  you  override  the	default  local delivery agent then you need to review the
       LOCAL_RECIPIENT_README document, otherwise the SMTP  server  may  reject  mail  for  local
       recipients.

luser_relay (default: empty)
       Optional  catch-all  destination  for  unknown  local(8) recipients.  By default, mail for
       unknown recipients in domains that match $mydestination, $inet_interfaces or $proxy_inter-
       faces is returned as undeliverable.

       The following $name expansions are done on luser_relay:

       $domain
	      The recipient domain.

       $extension
	      The recipient address extension.

       $home  The recipient's home directory.

       $local The entire recipient address localpart.

       $recipient
	      The full recipient address.

       $recipient_delimiter
	      The system-wide recipient address extension delimiter.

       $shell The recipient's login shell.

       $user  The recipient username.

       ${name?value}
	      Expands to value when $name has a non-empty value.

       ${name:value}
	      Expands to value when $name has an empty value.

       Instead of $name you can also specify ${name} or $(name).

       Note: luser_relay works only for the Postfix local(8) delivery agent.

       Note:  if  you  use this feature for accounts not in the UNIX password file, then you must
       specify "local_recipient_maps =" (i.e. empty) in the main.cf file, otherwise  the  Postfix
       SMTP  server  will reject mail for non-UNIX accounts with "User unknown in local recipient
       table".

       Examples:

       luser_relay = $user@other.host
       luser_relay = $local@other.host
       luser_relay = admin+$local

mail_name (default: Postfix)
       The mail system name that is displayed in Received: headers, in the SMTP greeting  banner,
       and in bounced mail.

mail_owner (default: postfix)
       The  UNIX  system  account  that owns the Postfix queue and most Postfix daemon processes.
       Specify the name of an unprivileged user account that does not share a user  or	group  ID
       with other accounts, and that owns no other files or processes on the system.  In particu-
       lar, don't specify nobody or daemon.  PLEASE USE A DEDICATED USER ID AND GROUP ID.

       When this parameter value is changed you need to re-run	"postfix  set-permissions"  (with
       Postfix version 2.0 and earlier: "/etc/postfix/post-install set-permissions".

mail_release_date (default: see postconf -d output)
       The Postfix release date, in "YYYYMMDD" format.

mail_spool_directory (default: see postconf -d output)
       The directory where local(8) UNIX-style mailboxes are kept. The default setting depends on
       the system type. Specify a name ending in / for maildir-style delivery.

       Note: maildir delivery is done with the privileges of  the  recipient.	If  you  use  the
       mail_spool_directory  setting  for  maildir  style delivery, then you must create the top-
       level maildir directory in advance. Postfix will not create it.

       Examples:

       mail_spool_directory = /var/mail
       mail_spool_directory = /var/spool/mail

mail_version (default: see postconf -d output)
       The version of the mail system. Stable releases are named major.minor.patchlevel.  Experi-
       mental  releases  also  include	the  release date. The version string can be used in, for
       example, the SMTP greeting banner.

mailbox_command (default: empty)
       Optional external command that the local(8) delivery agent should use for  mailbox  deliv-
       ery.   The  command  is	run  with  the user ID and the primary group ID privileges of the
       recipient.  Exception: command delivery for root executes with $default_privs  privileges.
       This  is  not  a problem, because 1) mail for root should always be aliased to a real user
       and 2) don't log in as root, use "su" instead.

       The following environment variables are exported to the command:

       CLIENT_ADDRESS
	      Remote client network address. Available in Postfix version 2.2 and later.

       CLIENT_HELO
	      Remote client EHLO command parameter. Available in Postfix version 2.2 and later.

       CLIENT_HOSTNAME
	      Remote client hostname. Available in Postfix version 2.2 and later.

       CLIENT_PROTOCOL
	      Remote client protocol. Available in Postfix version 2.2 and later.

       DOMAIN The domain part of the recipient address.

       EXTENSION
	      The optional address extension.

       HOME   The recipient home directory.

       LOCAL  The recipient address localpart.

       LOGNAME
	      The recipient's username.

       ORIGINAL_RECIPIENT
	      The entire recipient address, before any address rewriting or aliasing.

       RECIPIENT
	      The full recipient address.

       SASL_METHOD
	      SASL authentication method specified in the remote client AUTH  command.	Available
	      in Postfix version 2.2 and later.

       SASL_SENDER
	      SASL  sender address specified in the remote client MAIL FROM command. Available in
	      Postfix version 2.2 and later.

       SASL_USER
	      SASL username specified in the remote client AUTH command.   Available  in  Postfix
	      version 2.2 and later.

       SENDER The full sender address.

       SHELL  The recipient's login shell.

       USER   The recipient username.

       Unlike  other  Postfix configuration parameters, the mailbox_command parameter is not sub-
       jected to $name substitutions. This is to make it easier  to  specify  shell  syntax  (see
       example below).

       If  you	can, avoid shell meta characters because they will force Postfix to run an expen-
       sive shell process. If you're delivering via Procmail then running a shell  won't  make	a
       noticeable difference in the total cost.

       Note:  if you use the mailbox_command feature to deliver mail system-wide, you must set up
       an alias that forwards mail for root to a real user.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,	  mailbox_transport,	mailbox_command_maps,	 mailbox_command,
       home_mailbox,  mail_spool_directory,   fallback_transport_maps,	 fallback_transport   and
       luser_relay.

       Examples:

       mailbox_command = /some/where/procmail
       mailbox_command = /some/where/procmail -a "$EXTENSION"
       mailbox_command = /some/where/maildrop -d "$USER"
	       -f "$SENDER" "$EXTENSION"

mailbox_command_maps (default: empty)
       Optional  lookup  tables  with per-recipient external commands to use for local(8) mailbox
       delivery.  Behavior is as with mailbox_command.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,	  mailbox_transport,	mailbox_command_maps,	 mailbox_command,
       home_mailbox,  mail_spool_directory,   fallback_transport_maps,	 fallback_transport   and
       luser_relay.

mailbox_delivery_lock (default: see postconf -d output)
       How  to	lock  a  UNIX-style  local(8)  mailbox before attempting delivery.  For a list of
       available file locking methods, use the "postconf -l" command.

       This setting is ignored with maildir style delivery,  because  such  deliveries	are  safe
       without explicit locks.

       Note:  The  dotlock  method requires that the recipient UID or GID has write access to the
       parent directory of the mailbox file.

       Note: the default setting of this parameter is system dependent.

mailbox_size_limit (default: 51200000)
       The maximal size of any local(8) individual mailbox or maildir file, or zero  (no  limit).
       In  fact, this limits the size of any file that is written to upon local delivery, includ-
       ing files written by external commands that are executed by the local(8) delivery agent.

       This limit must not be smaller than the message size limit.

mailbox_transport (default: empty)
       Optional message delivery transport that the local(8) delivery agent should use for  mail-
       box  delivery  to  all  local recipients, whether or not they are found in the UNIX passwd
       database.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,	  mailbox_transport,	mailbox_command_maps,	 mailbox_command,
       home_mailbox,  mail_spool_directory,   fallback_transport_maps,	 fallback_transport   and
       luser_relay.

mailbox_transport_maps (default: empty)
       Optional  lookup tables with per-recipient message delivery transports to use for local(8)
       mailbox delivery, whether or not the recipients are found in the UNIX passwd database.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,	  mailbox_transport,	mailbox_command_maps,	 mailbox_command,
       home_mailbox,  mail_spool_directory,   fallback_transport_maps,	 fallback_transport   and
       luser_relay.

       For  safety  reasons, this feature does not allow $number substitutions in regular expres-
       sion maps.

       This feature is available in Postfix 2.3 and later.

mailq_path (default: see postconf -d output)
       Sendmail compatibility feature that  specifies  where  the  Postfix  mailq(1)  command  is
       installed. This command can be used to list the Postfix mail queue.

manpage_directory (default: see postconf -d output)
       Where the Postfix manual pages are installed.

maps_rbl_domains (default: empty)
       Obsolete feature: use the reject_rbl_client feature instead.

maps_rbl_reject_code (default: 554)
       The  numerical  Postfix	SMTP  server  response	code when a remote SMTP client request is
       blocked	by  the  reject_rbl_client,   reject_rhsbl_client,   reject_rhsbl_reverse_client,
       reject_rhsbl_sender or reject_rhsbl_recipient restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

masquerade_classes (default: envelope_sender, header_sender, header_recipient)
       What addresses are subject to address masquerading.

       By  default,  address  masquerading is limited to envelope sender addresses, and to header
       sender and header recipient addresses.  This allows you to use address masquerading  on	a
       mail gateway while still being able to forward mail to users on individual machines.

       Specify zero or more of: envelope_sender, envelope_recipient, header_sender, header_recip-
       ient

masquerade_domains (default: empty)
       Optional list of  domains  whose  subdomain  structure  will  be  stripped  off	in  email
       addresses.

       The list is processed left to right, and processing stops at the first match.  Thus,

	   masquerade_domains = foo.example.com example.com

       strips	 "user@any.thing.foo.example.com"    to    "user@foo.example.com",   but   strips
       "user@any.thing.else.example.com" to "user@example.com".

       A domain name prefixed with ! means do not masquerade this domain or its subdomains. Thus,

	   masquerade_domains = !foo.example.com example.com

       does not change "user@any.thing.foo.example.com"  or  "user@foo.example.com",  but  strips
       "user@any.thing.else.example.com" to "user@example.com".

       Note: with Postfix version 2.2, message header address masquerading happens only when mes-
       sage header address rewriting is enabled:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received  from  a	network  client  that  matches	$local_header_re-
	      write_clients,

       o      The  message  is	received  from	the network, and the remote_header_rewrite_domain
	      parameter specifies a non-empty value.

       To get the behavior before Postfix version 2.2,	specify  "local_header_rewrite_clients	=
       static:all".

       Example:

       masquerade_domains = $mydomain

masquerade_exceptions (default: empty)
       Optional  list  of  user  names	that are not subjected to address masquerading, even when
       their address matches $masquerade_domains.

       By default, address masquerading makes no exceptions.

       Specify a list of user names, "/file/name" or "type:table" patterns, separated  by  commas
       and/or  whitespace.  The  list is matched left to right, and the search stops on the first
       match. A "/file/name" pattern is replaced by its contents; a "type:table" lookup table  is
       matched	when  a  name matches a lookup key (the lookup result is ignored).  Continue long
       lines by starting the next line with whitespace. Specify "!pattern" to exclude a name from
       the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

       Examples:

       masquerade_exceptions = root, mailer-daemon
       masquerade_exceptions = root

master_service_disable (default: empty)
       Selectively  disable master(8) listener ports by service type or by service name and type.
       Specify a list of service types ("inet", "unix", "fifo", or "pass") or "name.type" tuples,
       where "name" is the first field of a master.cf entry and "type" is a service type. As with
       other Postfix matchlists, a search stops  at  the  first  match.   Specify  "!pattern"  to
       exclude a service from the list. By default, all master(8) listener ports are enabled.

       Note:  this  feature  does  not support "/file/name" or "type:table" patterns, nor does it
       support wildcards such as "*" or "all". This is intentional.

       Examples:

       # Turn on all master(8) listener ports (the default).
       master_service_disable =
       # Turn off only the main SMTP listener port.
       master_service_disable = smtp.inet
       # Turn off all TCP/IP listener ports.
       master_service_disable = inet
       # Turn off all TCP/IP listener ports except "foo".
       master_service_disable = !foo.inet, inet

       This feature is available in Postfix 2.6 and later.

max_idle (default: 100s)
       The maximum amount of time that an idle Postfix daemon process waits for an incoming  con-
       nection	before	terminating  voluntarily.  This parameter is ignored by the Postfix queue
       manager and by other long-lived Postfix daemon processes.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

max_use (default: 100)
       The  maximal  number  of  incoming  connections that a Postfix daemon process will service
       before terminating voluntarily.	This parameter is ignored by the  Postfix  queue  manager
       and by other long-lived Postfix daemon processes.

maximal_backoff_time (default: 4000s)
       The maximal time between attempts to deliver a deferred message.

       This  parameter	should	be set to a value greater than or equal to $minimal_backoff_time.
       See also $queue_run_delay.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

maximal_queue_lifetime (default: 5d)
       Consider  a  message as undeliverable, when delivery fails with a temporary error, and the
       time in the queue has reached the maximal_queue_lifetime limit.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is d (days).

       Specify 0 when mail delivery should be tried only once.

message_reject_characters (default: empty)
       The  set  of  characters  that  Postfix	will reject in message content.  The usual C-like
       escape sequences are recognized: \a \b \f \n \r \t \v \ddd (up to three octal digits)  and
       \\.

       Note  1: this feature does not recognize text that requires MIME decoding. It inspects raw
       message content, just like header_checks and body_checks.

       Note 2: this feature is disabled with "receive_override_options = no_header_body_checks".

       Example:

       message_reject_characters = \0

       This feature is available in Postfix 2.3 and later.

message_size_limit (default: 10240000)
       The maximal size in bytes of a message, including envelope information.

       Note: be careful when making changes.  Excessively small values will result in the loss of
       non-delivery  notifications,  when a bounce message size exceeds the local or remote MTA's
       message size limit.

message_strip_characters (default: empty)
       The set of characters that Postfix will remove from message  content.   The  usual  C-like
       escape  sequences are recognized: \a \b \f \n \r \t \v \ddd (up to three octal digits) and
       \\.

       Note 1: this feature does not recognize text that requires MIME decoding. It inspects  raw
       message content, just like header_checks and body_checks.

       Note 2: this feature is disabled with "receive_override_options = no_header_body_checks".

       Example:

       message_strip_characters = \0

       This feature is available in Postfix 2.3 and later.

milter_command_timeout (default: 30s)
       The  time limit for sending an SMTP command to a Milter (mail filter) application, and for
       receiving the response.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies the time unit).

       Time  units:  s	(seconds),  m (minutes), h (hours), d (days), w (weeks). The default time
       unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_connect_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after completion of an  SMTP
       connection. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_connect_timeout (default: 30s)
       The  time  limit for connecting to a Milter (mail filter) application, and for negotiating
       protocol options.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies the time unit).

       Time  units:  s	(seconds),  m (minutes), h (hours), d (days), w (weeks). The default time
       unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_content_timeout (default: 300s)
       The time limit for sending message content to a Milter (mail filter) application, and  for
       receiving the response.

       Specify	a  non-zero time value (an integral value plus an optional one-letter suffix that
       specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w  (weeks).  The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_data_macros (default: see postconf -d output)
       The  macros  that  are sent to version 4 or higher Milter (mail filter) applications after
       the SMTP DATA command. See MILTER_README for a list of available  macro	names  and  their
       meanings.

       This feature is available in Postfix 2.3 and later.

milter_default_action (default: tempfail)
       The  default  action when a Milter (mail filter) application is unavailable or mis-config-
       ured. Specify one of the following:

       accept Proceed as if the mail filter was not present.

       reject Reject all further commands in this session with a permanent status code.

       tempfail
	      Reject all further commands in this session with a temporary status code.

       quarantine
	      Like "accept", but freeze the message in the "hold" queue. Available  with  Postfix
	      2.6 and later.

       This feature is available in Postfix 2.3 and later.

milter_end_of_data_macros (default: see postconf -d output)
       The  macros  that  are sent to Milter (mail filter) applications after the message end-of-
       data. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_end_of_header_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the end of the message
       header. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.5 and later.

milter_header_checks (default: empty)
       Optional lookup tables for content inspection of message headers that are produced by Mil-
       ter applications.  See the header_checks(5)  manual  page  available  actions.  Currently,
       PREPEND is not implemented.

       The  following  example	sends all mail that is marked as SPAM to a spam handling machine.
       Note that matches are case-insensitive by default.

       /etc/postfix/main.cf:
	   milter_header_checks = pcre:/etc/postfix/milter_header_checks

       /etc/postfix/milter_header_checks:
	   /^X-SPAM-FLAG:\s+YES/ FILTER mysmtp:sanitizer.example.com:25

       The milter_header_checks mechanism could also be used for  whitelisting.  For  example  it
       could  be  used	to skip heavy content inspection for DKIM-signed mail from known friendly
       domains.

       This feature is available in Postfix 2.7, and as an optional patch for Postfix 2.6.

milter_helo_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the SMTP HELO or  EHLO
       command. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_macro_daemon_name (default: $myhostname)
       The  {daemon_name}  macro  value for Milter (mail filter) applications.	See MILTER_README
       for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_macro_v (default: $mail_name $mail_version)
       The {v} macro value for Milter (mail filter) applications.  See MILTER_README for  a  list
       of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_mail_macros (default: see postconf -d output)
       The  macros  that  are  sent to Milter (mail filter) applications after the SMTP MAIL FROM
       command. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_protocol (default: 6)
       The mail filter protocol version and optional protocol extensions for communication with a
       Milter  application;  prior  to	Postfix 2.6 the default protocol is 2. Postfix sends this
       version number during the initial protocol handshake.  It should match the version  number
       that is expected by the mail filter application (or by its Milter library).

       Protocol versions:

       2      Use  Sendmail  8 mail filter protocol version 2 (default with Sendmail version 8.11
	      .. 8.13 and Postfix version 2.3 ..  2.5).

       3      Use Sendmail 8 mail filter protocol version 3.

       4      Use Sendmail 8 mail filter protocol version 4.

       6      Use Sendmail 8 mail filter protocol version 6 (default with Sendmail  version  8.14
	      and Postfix version 2.6).

       Protocol extensions:

       no_header_reply
	      Specify this when the Milter application will not reply for each individual message
	      header.

       This feature is available in Postfix 2.3 and later.

milter_rcpt_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the SMTP RCPT TO  com-
       mand. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_unknown_command_macros (default: see postconf -d output)
       The macros that are sent to version 3 or higher Milter (mail filter) applications after an
       unknown SMTP command.  See MILTER_README for a list of available  macro	names  and  their
       meanings.

       This feature is available in Postfix 2.3 and later.

mime_boundary_length_limit (default: 2048)
       The  maximal  length  of  MIME multipart boundary strings. The MIME processor is unable to
       distinguish between boundary  strings  that  do	not  differ  in  the  first  $mime_bound-
       ary_length_limit characters.

       This feature is available in Postfix 2.0 and later.

mime_header_checks (default: $header_checks)
       Optional  lookup  tables  for  content  inspection  of  MIME  related  message headers, as
       described in the header_checks(5) manual page.

       This feature is available in Postfix 2.0 and later.

mime_nesting_limit (default: 100)
       The maximal recursion level that the MIME processor will  handle.   Postfix  refuses  mail
       that is nested deeper than the specified limit.

       This feature is available in Postfix 2.0 and later.

minimal_backoff_time (default: 300s)
       The  minimal time between attempts to deliver a deferred message; prior to Postfix 2.4 the
       default value was 1000s.

       This parameter also limits the time an unreachable destination is kept in the  short-term,
       in-memory, destination status cache.

       This  parameter	should	be set greater than or equal to $queue_run_delay. See also $maxi-
       mal_backoff_time.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

multi_instance_directories (default: empty)
       An  optional  list  of  non-default  Postfix  configuration directories; these directories
       belong to additional Postfix instances that share the Postfix executable files  and  docu-
       mentation with the default Postfix instance, and that are started, stopped, etc., together
       with the default Postfix instance.  Specify a list of  pathnames  separated  by	comma  or
       whitespace.

       When  $multi_instance_directories is empty, the postfix(1) command runs in single-instance
       mode and operates on a single Postfix instance only.  Otherwise,  the  postfix(1)  command
       runs  in  multi-instance  mode  and  invokes the multi-instance manager specified with the
       multi_instance_wrapper parameter. The multi-instance manager in turn  executes  postfix(1)
       commands  for the default instance and for all Postfix instances in $multi_instance_direc-
       tories.

       Currently, this parameter setting is ignored except for the default main.cf file.

       This feature is available in Postfix 2.6 and later.

multi_instance_enable (default: no)
       Allow this Postfix instance to be started, stopped, etc., by a multi-instance manager.  By
       default,  new  instances are created in a safe state that prevents them from being started
       inadvertently.  This parameter is reserved for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_group (default: empty)
       The optional instance group name of this Postfix instance.  A  group  identifies  closely-
       related	Postfix  instances  that  the  multi-instance manager can start, stop, etc., as a
       unit.  This parameter is reserved for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_name (default: empty)
       The optional instance name of this Postfix instance. This name becomes  also  the  default
       value for the syslog_name parameter.

       This feature is available in Postfix 2.6 and later.

multi_instance_wrapper (default: empty)
       The  pathname of a multi-instance manager command that the postfix(1) command invokes when
       the multi_instance_directories parameter value is non-empty. The pathname may be  followed
       by  initial command arguments separated by whitespace; shell metacharacters such as quotes
       are not supported in this context.

       The postfix(1) command invokes the manager command with the postfix(1) non-option  command
       arguments  on the manager command line, and with all installation configuration parameters
       exported into the manager command process environment. The manager command in turn invokes
       the  postfix(1)	command  for individual Postfix instances as "postfix -c config_directory
       command".

       This feature is available in Postfix 2.6 and later.

multi_recipient_bounce_reject_code (default: 550)
       The numerical Postfix SMTP server response code when  a	remote	SMTP  client  request  is
       blocked by the reject_multi_recipient_bounce restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.1 and later.

mydestination (default: $myhostname, localhost.$mydomain, localhost)
       The  list  of domains that are delivered via the $local_transport mail delivery transport.
       By default this is the Postfix local(8) delivery agent which looks up  all  recipients  in
       /etc/passwd   and  /etc/aliases.  The  SMTP  server  validates  recipient  addresses  with
       $local_recipient_maps and rejects non-existent recipients. See also the local domain class
       in the ADDRESS_CLASS_README file.

       The  default  mydestination  value  specifies names for the local machine only.	On a mail
       domain gateway, you should also include $mydomain.

       The  $local_transport  delivery	method	is  also   selected   for   mail   addressed   to
       user@[the.net.work.address]  of	the  mail  system  (the  IP  addresses specified with the
       inet_interfaces and proxy_interfaces parameters).

       Warnings:

       o      Do not specify the names of virtual domains - those  domains  are  specified  else-
	      where. See VIRTUAL_README for more information.

       o      Do  not  specify	the names of domains that this machine is backup MX host for. See
	      STANDARD_CONFIGURATION_README for how to set up backup MX hosts.

       o      By default, the Postfix SMTP server rejects mail for recipients not listed with the
	      local_recipient_maps  parameter.	 See  the postconf(5) manual for a description of
	      the local_recipient_maps and unknown_local_recipient_reject_code parameters.

       Specify a list of host or domain names, "/file/name" or "type:table"  patterns,	separated
       by  commas  and/or  whitespace.	A  "/file/name"  pattern  is  replaced by its contents; a
       "type:table" lookup table is matched when a name matches a lookup key (the  lookup  result
       is ignored).  Continue long lines by starting the next line with whitespace.

       Examples:

       mydestination = $myhostname, localhost.$mydomain $mydomain
       mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain

mydomain (default: see postconf -d output)
       The internet domain name of this mail system.  The default is to use $myhostname minus the
       first component, or "localdomain" (Postfix 2.3 and later).  $mydomain is used as a default
       value for many other configuration parameters.

       Example:

       mydomain = domain.tld

myhostname (default: see postconf -d output)
       The  internet  hostname	of  this  mail	system. The default is to use the fully-qualified
       domain name (FQDN) from gethostname(), or to use the non-FQDN  result  from  gethostname()
       and append ".$mydomain".  $myhostname is used as a default value for many other configura-
       tion parameters.

       Example:

       myhostname = host.example.com

mynetworks (default: see postconf -d output)
       The list of "trusted" remote SMTP clients that have more privileges than "strangers".

       In particular, "trusted" SMTP clients are allowed to relay mail through Postfix.  See  the
       smtpd_relay_restrictions parameter description in the postconf(5) manual.

       You  can specify the list of "trusted" network addresses by hand or you can let Postfix do
       it for you (which is the default).  See the description of the mynetworks_style	parameter
       for more information.

       If you specify the mynetworks list by hand, Postfix ignores the mynetworks_style setting.

       Specify	a  list  of  network  addresses  or network/netmask patterns, separated by commas
       and/or whitespace. Continue long lines by starting the next line with whitespace.

       The netmask specifies the number of bits in the network part of a host address.	 You  can
       also specify "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced by
       its contents; a "type:table" lookup table is matched when a table entry matches	a  lookup
       string (the lookup result is ignored).

       The  list  is  matched  left  to  right, and the search stops on the first match.  Specify
       "!pattern" to exclude an address or network block from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

       Note:  IP  version  6  address  information  must be specified inside [] in the mynetworks
       value, and in files specified with "/file/name".  IP version 6 addresses contain  the  ":"
       character, and would otherwise be confused with a "type:table" pattern.

       Examples:

       mynetworks = 127.0.0.0/8 168.100.189.0/28
       mynetworks = !192.168.0.1, 192.168.0.0/28
       mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
       mynetworks = $config_directory/mynetworks
       mynetworks = hash:/etc/postfix/network_table

mynetworks_style (default: subnet)
       The  method  to generate the default value for the mynetworks parameter.  This is the list
       of trusted networks for relay access control etc.

       o      Specify "mynetworks_style = host"  when  Postfix	should	"trust"  only  the  local
	      machine.

       o      Specify "mynetworks_style = subnet" when Postfix should "trust" remote SMTP clients
	      in the same IP subnetworks as the local machine.	On Linux,  this  works	correctly
	      only with interfaces specified with the "ifconfig" command.

       o      Specify  "mynetworks_style = class" when Postfix should "trust" remote SMTP clients
	      in the same IP class A/B/C networks as the local machine.  Don't	do  this  with	a
	      dialup  site  -  it  would cause Postfix to "trust" your entire provider's network.
	      Instead, specify an explicit mynetworks list by hand, as described with the  mynet-
	      works configuration parameter.

myorigin (default: $myhostname)
       The  domain  name  that	locally-posted mail appears to come from, and that locally posted
       mail is delivered to. The default, $myhostname, is adequate for small sites.  If you run a
       domain  with  multiple  machines, you should (1) change this to $mydomain and (2) set up a
       domain-wide alias database that aliases each user to user@that.users.mailhost.

       Example:

       myorigin = $mydomain

nested_header_checks (default: $header_checks)
       Optional lookup tables for content inspection of non-MIME message headers in attached mes-
       sages, as described in the header_checks(5) manual page.

       This feature is available in Postfix 2.0 and later.

newaliases_path (default: see postconf -d output)
       Sendmail  compatibility	feature that specifies the location of the newaliases(1) command.
       This command can be used to rebuild the local(8) aliases(5) database.

non_fqdn_reject_code (default: 504)
       The numerical Postfix SMTP server reply code when a client  request  is	rejected  by  the
       reject_non_fqdn_helo_hostname,	 reject_non_fqdn_sender    or	reject_non_fqdn_recipient
       restriction.

non_smtpd_milters (default: empty)
       A list of Milter (mail filter) applications for new mail that  does  not  arrive  via  the
       Postfix	smtpd(8) server. This includes local submission via the sendmail(1) command line,
       new mail that arrives via the Postfix qmqpd(8) server, and old mail  that  is  re-injected
       into  the  queue  with  "postsuper -r".	Specify space or comma as separator. See the MIL-
       TER_README document for details.

       This feature is available in Postfix 2.3 and later.

notify_classes (default: resource, software)
       The list of error classes that are reported to the postmaster. The default  is  to  report
       only  the most serious problems. The paranoid may wish to turn on the policy (UCE and mail
       relaying) and protocol error (broken mail software) reports.

       NOTE: postmaster notifications may contain confidential information such as SASL passwords
       or  message content.  It is the system administrator's responsibility to treat such infor-
       mation with care.

       The error classes are:

       bounce (also implies 2bounce)
	      Send the postmaster copies of the headers of bounced mail, and send transcripts  of
	      SMTP  sessions  when  Postfix rejects mail. The notification is sent to the address
	      specified with the bounce_notice_recipient configuration parameter (default:  post-
	      master).

       2bounce
	      Send  undeliverable bounced mail to the postmaster. The notification is sent to the
	      address  specified  with	the  2bounce_notice_recipient	configuration	parameter
	      (default: postmaster).

       data   Send the postmaster a transcript of the SMTP session with an error because a criti-
	      cal data file was unavailable. The notification is sent to  the  address	specified
	      with the error_notice_recipient configuration parameter (default: postmaster).
	      This feature is available in Postfix 2.9 and later.

       delay  Send the postmaster copies of the headers of delayed mail (see delay_warning_time).
	      The notification is sent to the address specified with  the  delay_notice_recipient
	      configuration parameter (default: postmaster).

       policy Send  the  postmaster  a	transcript  of the SMTP session when a client request was
	      rejected because of (UCE) policy. The notification is sent to the address specified
	      with the error_notice_recipient configuration parameter (default: postmaster).

       protocol
	      Send  the  postmaster  a transcript of the SMTP session in case of client or server
	      protocol errors. The notification  is  sent  to  the  address  specified	with  the
	      error_notice_recipient configuration parameter (default: postmaster).

       resource
	      Inform  the postmaster of mail not delivered due to resource problems.  The notifi-
	      cation is sent to the address specified with the error_notice_recipient  configura-
	      tion parameter (default: postmaster).

       software
	      Inform  the postmaster of mail not delivered due to software problems.  The notifi-
	      cation is sent to the address specified with the error_notice_recipient  configura-
	      tion parameter (default: postmaster).

       Examples:

       notify_classes = bounce, delay, policy, protocol, resource, software
       notify_classes = 2bounce, resource, software

owner_request_special (default: yes)
       Give  special  treatment  to owner-listname and listname-request address localparts: don't
       split such addresses when the recipient_delimiter is set to "-".  This feature  is  useful
       for mailing lists.

parent_domain_matches_subdomains (default: see postconf -d output)
       What Postfix features match subdomains of "domain.tld" automatically, instead of requiring
       an explicit ".domain.tld" pattern.  This is planned backwards compatibility:   eventually,
       all  Postfix  features  are expected to require explicit ".domain.tld" style patterns when
       you really want to match subdomains.

permit_mx_backup_networks (default: empty)
       Restrict the use of the permit_mx_backup SMTP access feature to only domains whose primary
       MX  hosts  match  the listed networks.  The parameter value syntax is the same as with the
       mynetworks parameter; note, however, that the default value is empty.

pickup_service_name (default: pickup)
       The name of the pickup(8) service. This service picks up local mail submissions	from  the
       Postfix maildrop queue.

       This feature is available in Postfix 2.0 and later.

plaintext_reject_code (default: 450)
       The  numerical  Postfix	SMTP  server  response	code  when  a  request is rejected by the
       reject_plaintext_session restriction.

       This feature is available in Postfix 2.3 and later.

postmulti_control_commands (default: reload flush)
       The postfix(1) commands that the postmulti(1) instance manager treats  as  "control"  com-
       mands,  that  operate  on  running  instances.  For these commands, disabled instances are
       skipped.

       This feature is available in Postfix 2.6 and later.

postmulti_start_commands (default: start)
       The postfix(1) commands that the postmulti(1) instance manager treats as "start" commands.
       For these commands, disabled instances are "checked" rather than "started", and failure to
       "start" a member instance of an instance group will abort the start-up of later instances.

       This feature is available in Postfix 2.6 and later.

postmulti_stop_commands (default: see postconf -d output)
       The postfix(1) commands that the postmulti(1) instance manager treats as "stop"	commands.
       For these commands, disabled instances are skipped, and enabled instances are processed in
       reverse order.

       This feature is available in Postfix 2.6 and later.

postscreen_access_list (default: permit_mynetworks)
       Permanent white/blacklist for remote SMTP client  IP  addresses.   postscreen(8)  searches
       this  list  immediately	after  a remote SMTP client connects.  Specify a comma- or white-
       space-separated list of commands (in upper or lower case) or  lookup  tables.  The  search
       stops upon the first command that fires for the client IP address.

	permit_mynetworks
	      Whitelist  the  client  and  terminate  the search if the client IP address matches
	      $mynetworks.  Do not subject the client to any  before/after  220  greeting  tests.
	      Pass the connection immediately to a Postfix SMTP server process.

	type:table
	      Query  the  specified  lookup  table.  Each  table lookup result is an access list,
	      except that access lists inside a table cannot specify type:table entries.
	      To discourage the use of hash, btree, etc. tables, there is  no  support	for  sub-
	      string matching like smtpd(8). Use CIDR tables instead.

	permit
	      Whitelist  the  client  and  terminate the search. Do not subject the client to any
	      before/after 220 greeting tests. Pass the connection immediately to a Postfix  SMTP
	      server process.

	reject
	      Blacklist  the  client  and  terminate the search. Subject the client to the action
	      configured with the postscreen_blacklist_action configuration parameter.

	dunno All postscreen(8) access lists implicitly have this command at the end.
	      When  dunno is executed inside a lookup table, return from  the  lookup  table  and
	      evaluate the next command.
	      When   dunno  is executed outside a lookup table, terminate the search, and subject
	      the client to the configured before/after 220 greeting tests.

       Example:

       /etc/postfix/main.cf:
	   postscreen_access_list = permit_mynetworks,
		 cidr:/etc/postfix/postscreen_access.cidr
	   postscreen_blacklist_action = enforce

       /etc/postfix/postscreen_access.cidr:
	   # Rules are evaluated in the order as specified.
	   # Blacklist 192.168.* except 192.168.0.1.
	   192.168.0.1	       dunno
	   192.168.0.0/16      reject

       This feature is available in Postfix 2.8.

postscreen_bare_newline_action (default: ignore)
       The action that postscreen(8) takes when a remote SMTP client sends a bare newline charac-
       ter, that is, a newline not preceded by carriage return.  Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to complete.  Do not repeat this
	      test before some the result from some other test expires.  This  option  is  useful
	      for testing and collecting statistics without blocking mail permanently.

       enforce
	      Allow  other  tests  to  complete.  Reject attempts to deliver mail with a 550 SMTP
	      reply, and log the helo/sender/recipient information.  Repeat this  test	the  next
	      time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat this test the next
	      time the client connects.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_enable (default: no)
       Enable "bare newline" SMTP protocol tests in the postscreen(8)  server.	These  tests  are
       expensive:  a  remote  SMTP client must disconnect after it passes the test, before it can
       talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_ttl (default: 30d)
       The amount of time that postscreen(8) will use the result from a successful "bare newline"
       SMTP  protocol  test.  During this time, the client IP address is excluded from this test.
       The default is long because a remote SMTP client must disconnect after it passes the test,
       before it can talk to a real Postfix SMTP server.

       Specify	a  non-zero time value (an integral value plus an optional one-letter suffix that
       specifies the time unit).  Time units: s (seconds), m (minutes), h (hours),  d  (days),	w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_blacklist_action (default: ignore)
       The  action  that postscreen(8) takes when a remote SMTP client is permanently blacklisted
       with the postscreen_access_list parameter.  Specify one of the following:

       ignore (default)
	      Ignore  this result. Allow other tests to complete.  Repeat this test the next time
	      the  client  connects.  This option is useful for testing and collecting statistics
	      without blocking mail.

       enforce
	      Allow other tests to complete. Reject attempts to deliver  mail  with  a	550  SMTP
	      reply,  and  log	the helo/sender/recipient information.	Repeat this test the next
	      time the client connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat this  test	the  next
	      time the client connects.

       This feature is available in Postfix 2.8.

postscreen_cache_cleanup_interval (default: 12h)
       The  amount of time between postscreen(8) cache cleanup runs.  Cache cleanup increases the
       load on the cache database and should  therefore  not  be  run  frequently.  This  feature
       requires  that the cache database supports the "delete" and "sequence" operators.  Specify
       a zero interval to disable cache cleanup.

       After each cache cleanup run, the postscreen(8) daemon logs the	number	of  entries  that
       were retained and dropped. A cleanup run is logged as "partial" when the daemon terminates
       early after "postfix reload", "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_cache_map (default: btree:$data_directory/postscreen_cache)
       Persistent storage for the postscreen(8) server decisions.

       To  share  a  postscreen(8)  cache   between   multiple	 postscreen(8)	 instances,   use
       "postscreen_cache_map  = proxy:btree:/path/to/file".  This requires Postfix version 2.9 or
       later; earlier proxymap(8) implementations don't support cache cleanup. For an alternative
       approach see the memcache_table(5) manpage.

       This feature is available in Postfix 2.8.

postscreen_cache_retention_time (default: 7d)
       The  amount  of	time  that  postscreen(8) will cache an expired temporary whitelist entry
       before it is removed. This prevents clients from being logged as "NEW" just because  their
       cache  entry  expired an hour ago. It also prevents the cache from filling up with clients
       that passed some deep protocol test once and never came back.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_client_connection_count_limit (default: $smtpd_client_connection_count_limit)
       How many simultaneous connections any remote SMTP client  is  allowed  to  have	with  the
       postscreen(8)  daemon. By default, this limit is the same as with the Postfix SMTP server.
       Note  that  the	triage	process  can  take  several  seconds,  with  the  time	spent  in
       postscreen_greet_wait delay, and with the time spent talking to the postscreen(8) built-in
       dummy SMTP protocol engine.

       This feature is available in Postfix 2.8.

postscreen_command_count_limit (default: 20)
       The limit on the total number of commands per SMTP session  for	postscreen(8)'s  built-in
       SMTP  protocol  engine.	 This SMTP engine defers or rejects all attempts to deliver mail,
       therefore there is no need to enforce separate limits on the number of junk  commands  and
       error commands.

       This feature is available in Postfix 2.8.

postscreen_command_filter (default: $smtpd_command_filter)
       A  mechanism to transform commands from remote SMTP clients.  See smtpd_command_filter for
       further details.

       This feature is available in Postfix 2.8 and later.

postscreen_command_time_limit (default: ${stress?10}${stress:300}s)
       The time limit to read an entire command line with postscreen(8)'s built-in SMTP  protocol
       engine.

       This feature is available in Postfix 2.8.

postscreen_disable_vrfy_command (default: $disable_vrfy_command)
       Disable	the  SMTP VRFY command in the postscreen(8) daemon.  See disable_vrfy_command for
       details.

       This feature is available in Postfix 2.8.

postscreen_discard_ehlo_keyword_address_maps (default: $smtpd_discard_ehlo_keyword_address_maps)
       Lookup tables, indexed by the remote SMTP client address, with case insensitive	lists  of
       EHLO  keywords  (pipelining,  starttls, auth, etc.) that the postscreen(8) server will not
       send in the EHLO response to a remote SMTP  client.  See  smtpd_discard_ehlo_keywords  for
       details.  The table is not searched by hostname for robustness reasons.

       This feature is available in Postfix 2.8 and later.

postscreen_discard_ehlo_keywords (default: $smtpd_discard_ehlo_keywords)
       A  case	insensitive  list  of  EHLO  keywords (pipelining, starttls, auth, etc.) that the
       postscreen(8) server will not send in the EHLO response	to  a  remote  SMTP  client.  See
       smtpd_discard_ehlo_keywords for details.

       This feature is available in Postfix 2.8 and later.

postscreen_dnsbl_action (default: ignore)
       The  action  that  postscreen(8) takes when a remote SMTP client's combined DNSBL score is
       equal to or greater than a threshold  (as  defined  with  the  postscreen_dnsbl_sites  and
       postscreen_dnsbl_threshold parameters).	Specify one of the following:

       ignore (default)
	      Ignore  the  failure of this test. Allow other tests to complete.  Repeat this test
	      the next time the client connects.  This option is useful for testing and  collect-
	      ing statistics without blocking mail.

       enforce
	      Allow  other  tests  to  complete.  Reject attempts to deliver mail with a 550 SMTP
	      reply, and log the helo/sender/recipient information.  Repeat this  test	the  next
	      time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat this test the next
	      time the client connects.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_reply_map (default: empty)
       A mapping from actual DNSBL domain name which includes a secret	password,  to  the  DNSBL
       domain  name  that  postscreen  will  reply with when it rejects mail.  When no mapping is
       found, the actual DNSBL domain will be used.

       For maximal stability it is best to use a file that is read into  memory  such  as  pcre:,
       regexp:	or  texthash:  (texthash:  is similar to hash:, except a) there is no need to run
       postmap(1) before the file can be used, and b) texthash: does not detect changes after the
       file is read).

       Example:

       /etc/postfix/main.cf:
	   postscreen_dnsbl_reply_map = texthash:/etc/postfix/dnsbl_reply

       /etc/postfix/dnsbl_reply:
	  secret.zen.spamhaus.org    zen.spamhaus.org

       This feature is available in Postfix 2.8.

postscreen_dnsbl_sites (default: empty)
       Optional list of DNS white/blacklist domains, filters and weight factors. When the list is
       non-empty, the dnsblog(8) daemon will query these domains with the IP addresses of  remote
       SMTP  clients,  and  postscreen(8) will update an SMTP client's DNSBL score with each non-
       error reply.

       Caution: when postscreen rejects mail, it replies with the  DNSBL  domain  name.  Use  the
       postscreen_dnsbl_reply_map feature to hide "password" information in DNSBL domain names.

       When  a	client's  score  is  equal  to	or  greater  than  the	threshold  specified with
       postscreen_dnsbl_threshold, postscreen(8) can drop the connection  with	the  remote  SMTP
       client.

       Specify a list of domain=filter*weight entries, separated by comma or whitespace.

       o      When  no	"=filter" is specified, postscreen(8) will use any non-error DNSBL reply.
	      Otherwise, postscreen(8) uses only DNSBL replies that match the filter. The  filter
	      has  the	form  d.d.d.d, where each d is a number, or a pattern inside [] that con-
	      tains one or more ";"-separated numbers or number..number ranges.

       o      When no "*weight" is specified, postscreen(8) increments the remote  SMTP  client's
	      DNSBL  score  by	1.   Otherwise,  the  weight  must  be	an  integral  number, and
	      postscreen(8) adds the specified weight to the remote SMTP  client's  DNSBL  score.
	      Specify a negative number for whitelisting.

       o      When   one   postscreen_dnsbl_sites   entry   produces  multiple	DNSBL  responses,
	      postscreen(8) applies the weight at most once.

       Examples:

       To use example.com as a high-confidence blocklist, and to block mail with example.net  and
       example.org only when both agree:

       postscreen_dnsbl_threshold = 2
       postscreen_dnsbl_sites = example.com*2, example.net, example.org

       To filter only DNSBL replies containing 127.0.0.4:

       postscreen_dnsbl_sites = example.com=127.0.0.4

       This feature is available in Postfix 2.8.

postscreen_dnsbl_threshold (default: 1)
       The  inclusive  lower bound for blocking a remote SMTP client, based on its combined DNSBL
       score as defined with the postscreen_dnsbl_sites parameter.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_ttl (default: 1h)
       The amount of time that postscreen(8) will use the result from a successful DNS	blocklist
       test.  During  this time, the client IP address is excluded from this test. The default is
       relatively short, because a good client can  immediately  talk  to  a  real  Postfix  SMTP
       server.

       Specify	a  non-zero time value (an integral value plus an optional one-letter suffix that
       specifies the time unit).  Time units: s (seconds), m (minutes), h (hours),  d  (days),	w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_enforce_tls (default: $smtpd_enforce_tls)
       Mandatory  TLS: announce STARTTLS support to remote SMTP clients, and require that clients
       use TLS encryption.  See smtpd_postscreen_enforce_tls for details.

       This feature is available in Postfix 2.8 and later.  Preferably, use  postscreen_tls_secu-
       rity_level instead.

postscreen_expansion_filter (default: see postconf -d output)
       List  of  characters  that are permitted in postscreen_reject_footer attribute expansions.
       See smtpd_expansion_filter for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_forbidden_commands (default: $smtpd_forbidden_commands)
       List of commands that the postscreen(8) server considers in violation of the  SMTP  proto-
       col.  See  smtpd_forbidden_commands for syntax, and postscreen_non_smtp_command_action for
       possible actions.

       This feature is available in Postfix 2.8.

postscreen_greet_action (default: ignore)
       The action that postscreen(8) takes when a remote  SMTP	client	speaks	before	its  turn
       within  the  time  specified with the postscreen_greet_wait parameter.  Specify one of the
       following:

       ignore (default)
	      Ignore the failure of this test. Allow other tests to complete.  Repeat  this  test
	      the  next time the client connects.  This option is useful for testing and collect-
	      ing statistics without blocking mail.

       enforce
	      Allow other tests to complete. Reject attempts to deliver  mail  with  a	550  SMTP
	      reply,  and  log	the helo/sender/recipient information.	Repeat this test the next
	      time the client connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat this  test	the  next
	      time the client connects.

       In either case, postscreen(8) will not whitelist the remote SMTP client IP address.

       This feature is available in Postfix 2.8.

postscreen_greet_banner (default: $smtpd_banner)
       The  text  in the optional "220-text..." server response that postscreen(8) sends ahead of
       the real Postfix SMTP server's "220 text..." response, in an attempt to confuse	bad  SMTP
       clients	so that they speak before their turn (pre-greet).  Specify an empty value to dis-
       able this feature.

       This feature is available in Postfix 2.8.

postscreen_greet_ttl (default: 1d)
       The amount of time that postscreen(8) will use the result from a successful PREGREET test.
       During  this  time, the client IP address is excluded from this test. The default is rela-
       tively short, because a good client can immediately talk to a real Postfix SMTP server.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_greet_wait (default: ${stress?2}${stress:6}s)
       The amount of time that postscreen(8) will wait for an  SMTP  client  to  send  a  command
       before  its turn, and for DNS blocklist lookup results to arrive (default: up to 2 seconds
       under stress, up to 6 seconds otherwise).

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_helo_required (default: $smtpd_helo_required)
       Require that a remote SMTP client sends HELO or EHLO before commencing a MAIL transaction.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_action (default: drop)
       The  action  that postscreen(8) takes when a remote SMTP client sends non-SMTP commands as
       specified with the postscreen_forbidden_commands parameter.  Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to complete.  Do not repeat this
	      test  before  some  the result from some other test expires.  This option is useful
	      for testing and collecting statistics without blocking mail permanently.

       enforce
	      Allow other tests to complete. Reject attempts to deliver  mail  with  a	550  SMTP
	      reply,  and  log	the helo/sender/recipient information.	Repeat this test the next
	      time the client connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat this  test	the  next
	      time the client connects. This action is the same as with the Postfix SMTP server's
	      smtpd_forbidden_commands feature.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_enable (default: no)
       Enable "non-SMTP command" tests in the postscreen(8) server. These tests are expensive:	a
       client must disconnect after it passes the test, before it can talk to a real Postfix SMTP
       server.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_ttl (default: 30d)
       The amount of time that postscreen(8) will use the result from a successful "non_smtp_com-
       mand"  SMTP  protocol  test. During this time, the client IP address is excluded from this
       test. The default is long because a client must	disconnect  after  it  passes  the  test,
       before it can talk to a real Postfix SMTP server.

       Specify	a  non-zero time value (an integral value plus an optional one-letter suffix that
       specifies the time unit).  Time units: s (seconds), m (minutes), h (hours),  d  (days),	w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_pipelining_action (default: enforce)
       The  action  that  postscreen(8)  takes	when a remote SMTP client sends multiple commands
       instead of sending one command and waiting for the server to respond.  Specify one of  the
       following:

       ignore Ignore the failure of this test. Allow other tests to complete.  Do not repeat this
	      test before some the result from some other test expires.  This  option  is  useful
	      for testing and collecting statistics without blocking mail permanently.

       enforce
	      Allow  other  tests  to  complete.  Reject attempts to deliver mail with a 550 SMTP
	      reply, and log the helo/sender/recipient information.  Repeat this  test	the  next
	      time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat this test the next
	      time the client connects.

       This feature is available in Postfix 2.8.

postscreen_pipelining_enable (default: no)
       Enable "pipelining" SMTP protocol tests in  the	postscreen(8)  server.	These  tests  are
       expensive: a good client must disconnect after it passes the test, before it can talk to a
       real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_pipelining_ttl (default: 30d)
       The amount of time that postscreen(8) will use the result from a  successful  "pipelining"
       SMTP  protocol  test.  During this time, the client IP address is excluded from this test.
       The default is long because a good client must disconnect after it passes the test, before
       it can talk to a real Postfix SMTP server.

       Specify	a  non-zero time value (an integral value plus an optional one-letter suffix that
       specifies the time unit).  Time units: s (seconds), m (minutes), h (hours),  d  (days),	w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_post_queue_limit (default: $default_process_limit)
       The  number  of	clients  that  can be waiting for service from a real Postfix SMTP server
       process. When this queue is full, all clients will receive a 421 response.

       This feature is available in Postfix 2.8.

postscreen_pre_queue_limit (default: $default_process_limit)
       The number of non-whitelisted clients that can be waiting for a decision whether they will
       receive service from a real Postfix SMTP server process. When this queue is full, all non-
       whitelisted clients will receive a 421 response.

       This feature is available in Postfix 2.8.

postscreen_reject_footer (default: $smtpd_reject_footer)
       Optional information that is appended after a 4XX or 5XX  postscreen(8)	server	response.
       See smtpd_reject_footer for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_tls_security_level (default: $smtpd_tls_security_level)
       The SMTP TLS security level for the postscreen(8) server; when a non-empty value is speci-
       fied,	this	overrides    the    obsolete	parameters     postscreen_use_tls     and
       postscreen_enforce_tls. See smtpd_tls_security_level for details.

       This feature is available in Postfix 2.8 and later.

postscreen_upstream_proxy_protocol (default: empty)
       The  name  of the proxy protocol used by an optional before-postscreen proxy agent. When a
       proxy agent is used, this protocol conveys local and remote address and port  information.
       Specify "postscreen_upstream_proxy_protocol = haproxy" to enable the haproxy protocol.

       This feature is available in Postfix 2.10 and later.

postscreen_upstream_proxy_timeout (default: 5s)
       The  time limit for the proxy protocol specified with the postscreen_upstream_proxy_proto-
       col parameter.

       This feature is available in Postfix 2.10 and later.

postscreen_use_tls (default: $smtpd_use_tls)
       Opportunistic TLS: announce STARTTLS support to remote SMTP clients, but  do  not  require
       that clients use TLS encryption.

       This  feature is available in Postfix 2.8 and later.  Preferably, use postscreen_tls_secu-
       rity_level instead.

postscreen_watchdog_timeout (default: 10s)
       How much time a postscreen(8) process may take to respond to a remote SMTP client  command
       or  to  perform	a  cache  operation before it is terminated by a built-in watchdog timer.
       This is a safety mechanism that prevents postscreen(8) from becoming non-responsive due to
       a  bug  in  Postfix  itself  or in system software.  To avoid false alarms and unnecessary
       cache corruption this limit cannot be set under 10s.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_whitelist_interfaces (default: static:all)
       A list of local postscreen(8) server IP addresses  where  a  non-whitelisted  remote  SMTP
       client  can  obtain  postscreen(8)'s  temporary	whitelist status. This status is required
       before the client can talk to a Postfix SMTP server process.  By  default,  a  client  can
       obtain postscreen(8)'s whitelist status on any local postscreen(8) server IP address.

       When   postscreen(8)   listens	on   both   primary   and   backup   MX   addresses,  the
       postscreen_whitelist_interfaces	parameter  can	be  configured	to  give  the	temporary
       whitelist  status  only	when  a client connects to a primary MX address. Once a client is
       whitelisted it can talk to a Postfix SMTP server on any address. Thus, clients  that  con-
       nect  only to backup MX addresses will never become whitelisted, and will never be allowed
       to talk to a Postfix SMTP server process.

       Specify a list of network addresses  or	network/netmask  patterns,  separated  by  commas
       and/or  whitespace. The netmask specifies the number of bits in the network part of a host
       address. Continue long lines by starting the next line with whitespace.

       You can also specify "/file/name" or "type:table" patterns.   A	"/file/name"  pattern  is
       replaced  by  its  contents;  a	"type:table"  lookup  table is matched when a table entry
       matches a lookup string (the lookup result is ignored).

       The list is matched left to right, and the search stops on the first match. Specify "!pat-
       tern" to exclude an address or network block from the list.

       Note:   IP   version   6   address   information  must  be  specified  inside  []  in  the
       postscreen_whitelist_interfaces value, and in files specified with "/file/name".  IP  ver-
       sion  6	addresses  contain  the  ":"  character,  and  would otherwise be confused with a
       "type:table" pattern.

       Example:

       /etc/postfix/main.cf:
	   # Don't whitelist connections to the backup IP address.
	   postscreen_whitelist_interfaces = !168.100.189.8, static:all

       This feature is available in Postfix 2.9 and later.

prepend_delivered_header (default: command, file, forward)
       The message delivery contexts where the Postfix local(8) delivery agent prepends a  Deliv-
       ered-To:  message header with the address that the mail was delivered to. This information
       is used for mail delivery loop detection.

       By default, the Postfix local delivery agent prepends a Delivered-To: header when forward-
       ing  mail and when delivering to file (mailbox) and command. Turning off the Delivered-To:
       header when forwarding mail is not recommended.

       Specify zero or more of forward, file, or command.

       Example:

       prepend_delivered_header = forward

process_id (read-only)
       The process ID of a Postfix command or daemon process.

process_id_directory (default: pid)
       The location of Postfix PID files relative  to  $queue_directory.   This  is  a	read-only
       parameter.

process_name (read-only)
       The process name of a Postfix command or daemon process.

propagate_unmatched_extensions (default: canonical, virtual)
       What  address  lookup  tables  copy an address extension from the lookup key to the lookup
       result.

       For example, with a virtual(5) mapping of "joe@example.com =>  joe.user@example.net",  the
       address "joe+foo@example.com" would rewrite to "joe.user+foo@example.net".

       Specify	zero  or  more	of  canonical, virtual, alias, forward, include or generic. These
       cause address extension propagation with canonical(5), virtual(5),  and	aliases(5)  maps,
       with  local(8) .forward and :include: file lookups, and with smtp(8) generic maps, respec-
       tively.

       Note: enabling this feature for types other than canonical and virtual is likely to  cause
       problems  when  mail  is  forwarded to other sites, especially with mail that is sent to a
       mailing list exploder address.

       Examples:

       propagate_unmatched_extensions = canonical, virtual, alias,
	       forward, include
       propagate_unmatched_extensions = canonical, virtual

proxy_interfaces (default: empty)
       The network interface addresses that this mail system receives mail on by way of  a  proxy
       or network address translation unit.

       This feature is available in Postfix 2.0 and later.

       You  must  specify your "outside" proxy/NAT addresses when your system is a backup MX host
       for other domains, otherwise mail delivery loops will happen when the primary MX  host  is
       down.

       Example:

       proxy_interfaces = 1.2.3.4

proxy_read_maps (default: see postconf -d output)
       The  lookup tables that the proxymap(8) server is allowed to access for the read-only ser-
       vice.  Table references that don't begin with proxy: are ignored.

       This feature is available in Postfix 2.0 and later.

proxy_write_maps (default: see postconf -d output)
       The lookup tables that the proxymap(8) server is allowed to access for the read-write ser-
       vice.  Postfix-owned  local  database  files  should  be  stored  under	the Postfix-owned
       data_directory.	Table references that don't begin with proxy: are ignored.

       This feature is available in Postfix 2.5 and later.

proxymap_service_name (default: proxymap)
       The name of the proxymap read-only table lookup service.  This service is normally  imple-
       mented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

proxywrite_service_name (default: proxywrite)
       The  name  of  the  proxywrite  read-write table lookup service.  This service is normally
       implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

qmgr_clog_warn_time (default: 300s)
       The minimal delay between warnings that a specific destination is clogging up the  Postfix
       active queue. Specify 0 to disable.

       This feature is enabled with the helpful_warnings parameter.

       This feature is available in Postfix 2.0 and later.

qmgr_daemon_timeout (default: 1000s)
       How  much  time	a Postfix queue manager process may take to handle a request before it is
       terminated by a built-in watchdog timer.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_fudge_factor (default: 100)
       Obsolete feature: the percentage of delivery resources that a busy mail system will use up
       for delivery of a large mailing	list message.

       This feature exists only in the oqmgr(8) old queue  manager.  The  current  queue  manager
       solves the problem in a better way.

qmgr_ipc_timeout (default: 60s)
       The  time limit for the queue manager to send or receive information over an internal com-
       munication channel.  The purpose is to break out of deadlock situations. If the time limit
       is exceeded the software either retries or aborts the operation.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_message_active_limit (default: 20000)
       The maximal number of messages in the active queue.

qmgr_message_recipient_limit (default: 20000)
       The maximal number of recipients held in memory by the Postfix queue manager, and the max-
       imal size of the short-term, in-memory "dead" destination status cache.

qmgr_message_recipient_minimum (default: 10)
       The  minimal  number of in-memory recipients for any message. This takes priority over any
       other in-memory recipient limits (i.e., the global  qmgr_message_recipient_limit  and  the
       per transport _recipient_limit) if necessary. The minimum value allowed for this parameter
       is 1.

qmqpd_authorized_clients (default: empty)
       What remote QMQP clients are allowed to connect to the Postfix QMQP server port.

       By default, no client is allowed to use the service. This is because the QMQP server  will
       relay mail to any destination.

       Specify a list of client patterns. A list pattern specifies a host name, a domain name, an
       internet address, or a network/mask pattern, where the mask specifies the number  of  bits
       in  the	network part.  When a pattern specifies a file name, its contents are substituted
       for the file name; when a pattern is a "type:table" table specification, table  lookup  is
       used instead.

       Patterns  are  separated by whitespace and/or commas. In order to reverse the result, pre-
       cede a pattern with an exclamation point (!). The form "!/file/name" is supported only  in
       Postfix version 2.4 and later.

       Example:

       qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

qmqpd_client_port_logging (default: no)
       Enable  logging of the remote QMQP client port in addition to the hostname and IP address.
       The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

qmqpd_error_delay (default: 1s)
       How long the Postfix QMQP server will pause before sending a negative reply to the  remote
       QMQP client. The purpose is to slow down confused or malicious clients.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

qmqpd_timeout (default: 300s)
       The time limit for sending or receiving information over the network.  If a read or  write
       operation blocks for more than $qmqpd_timeout seconds the Postfix QMQP server gives up and
       disconnects.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

queue_directory (default: see postconf -d output)
       The location of the Postfix top-level queue directory. This is the root directory of Post-
       fix daemon processes that run chrooted.

queue_file_attribute_count_limit (default: 100)
       The maximal number of (name=value) attributes that may be stored in a Postfix queue  file.
       The limit is enforced by the cleanup(8) server.

       This feature is available in Postfix 2.0 and later.

queue_minfree (default: 0)
       The  minimal  amount  of  free  space  in bytes in the queue file system that is needed to
       receive mail.  This is currently used by the Postfix SMTP server  to  decide  if  it  will
       accept any mail at all.

       By  default,  the  Postfix  SMTP server rejects MAIL FROM commands when the amount of free
       space is less than 1.5*$message_size_limit (Postfix version 2.1 and later).  To specify	a
       higher  minimum free space limit, specify a queue_minfree value that is at least 1.5*$mes-
       sage_size_limit.

       With Postfix versions 2.0 and earlier, a queue_minfree value of zero  means  there  is  no
       minimum required amount of free space.

queue_run_delay (default: 300s)
       The  time  between  deferred  queue  scans  by the queue manager; prior to Postfix 2.4 the
       default value was 1000s.

       This parameter should be set less than or equal to $minimal_backoff_time. See also  $maxi-
       mal_backoff_time.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

queue_service_name (default: qmgr)
       The name of the qmgr(8) service. This service manages  the  Postfix  queue  and	schedules
       delivery requests.

       This feature is available in Postfix 2.0 and later.

rbl_reply_maps (default: empty)
       Optional  lookup  tables  with  RBL  response templates. The tables are indexed by the RBL
       domain name. By	default,  Postfix  uses  the  default  template  as  specified	with  the
       default_rbl_reply configuration parameter. See there for a discussion of the syntax of RBL
       reply templates.

       This feature is available in Postfix 2.0 and later.

readme_directory (default: see postconf -d output)
       The location of Postfix README files that describe how to build, configure  or  operate	a
       specific Postfix subsystem or feature.

receive_override_options (default: empty)
       Enable  or  disable  recipient validation, built-in content filtering, or address mapping.
       Typically, these are specified in master.cf as command-line arguments  for  the	smtpd(8),
       qmqpd(8) or pickup(8) daemons.

       Specify	zero or more of the following options.	The options override main.cf settings and
       are either implemented by smtpd(8), qmqpd(8), or pickup(8) themselves, or  they	are  for-
       warded to the cleanup server.

       no_unknown_recipient_checks
	      Do  not  try  to	reject	unknown recipients (SMTP server only).	This is typically
	      specified AFTER an external content filter.

       no_address_mappings
	      Disable canonical address mapping, virtual alias map expansion, address  masquerad-
	      ing,  and automatic BCC (blind carbon-copy) recipients. This is typically specified
	      BEFORE an external content filter.

       no_header_body_checks
	      Disable header/body_checks. This is typically specified AFTER an	external  content
	      filter.

       no_milters
	      Disable  Milter  (mail  filter)  applications. This is typically specified AFTER an
	      external content filter.

       Note: when the "BEFORE content filter" receive_override_options setting	is  specified  in
       the  main.cf  file, specify the "AFTER content filter" receive_override_options setting in
       master.cf (and vice versa).

       Examples:

       receive_override_options =
	   no_unknown_recipient_checks, no_header_body_checks
       receive_override_options = no_address_mappings

       This feature is available in Postfix 2.1 and later.

recipient_bcc_maps (default: empty)
       Optional BCC (blind carbon-copy) address lookup tables, indexed by recipient address.  The
       BCC address (multiple results are not supported) is added when mail enters from outside of
       Postfix.

       This feature is available in Postfix 2.1 and later.

       The table search order is as follows:

       o      Look up the "user+extension@domain.tld"  address	including  the	optional  address
	      extension.

       o      Look up the "user@domain.tld" address without the optional address extension.

       o      Look  up	the  "user+extension" address local part when the recipient domain equals
	      $myorigin, $mydestination, $inet_interfaces or $proxy_interfaces.

       o      Look up the "user" address local part when the recipient domain  equals  $myorigin,
	      $mydestination, $inet_interfaces or $proxy_interfaces.

       o      Look up the "@domain.tld" part.

       Specify	the  types  and names of databases to use.  After change, run "postmap /etc/post-
       fix/recipient_bcc".

       Note: with Postfix 2.3 and later the BCC address is added as  if  it  was  specified  with
       NOTIFY=NONE.  The  sender  will	not be notified when the BCC address is undeliverable, as
       long as all down-stream software implements RFC 3461.

       Note: with Postfix 2.2 and earlier the sender will be notified when  the  BCC  address  is
       undeliverable.

       Note:  automatic  BCC  recipients  are produced only for new mail.  To avoid mailer loops,
       automatic BCC recipients are not generated after  Postfix  forwards  mail  internally,  or
       after Postfix generates mail itself.

       Example:

       recipient_bcc_maps = hash:/etc/postfix/recipient_bcc

recipient_canonical_classes (default: envelope_recipient, header_recipient)
       What  addresses	are  subject  to  recipient_canonical_maps  address mapping.  By default,
       recipient_canonical_maps address mapping is applied to envelope recipient  addresses,  and
       to header recipient addresses.

       Specify one or more of: envelope_recipient, header_recipient

       This feature is available in Postfix 2.2 and later.

recipient_canonical_maps (default: empty)
       Optional  address  mapping lookup tables for envelope and header recipient addresses.  The
       table format and lookups are documented in canonical(5).

       Note: $recipient_canonical_maps is processed before $canonical_maps.

       Example:

       recipient_canonical_maps = hash:/etc/postfix/recipient_canonical

recipient_delimiter (default: empty)
       The separator between user names and address  extensions  (user+foo).   See  canonical(5),
       local(8), relocated(5) and virtual(5) for the effects this has on aliases, canonical, vir-
       tual, relocated and on .forward file lookups.  Basically, the software tries user+foo  and
       .forward+foo before trying user and .forward.

       Example:

       recipient_delimiter = +

reject_code (default: 554)
       The  numerical  Postfix	SMTP  server  response	code when a remote SMTP client request is
       rejected by the "reject" restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

reject_tempfail_action (default: defer_if_permit)
       The Postfix SMTP server's action when a reject-type restriction fails due to  a	temporary
       error condition. Specify "defer" to defer the remote SMTP client request immediately. With
       the default "defer_if_permit" action, the Postfix SMTP server continues to look for oppor-
       tunities  to  reject  mail,  and  defers  the client request only if it would otherwise be
       accepted.

       For  finer  control,  see:  unverified_recipient_tempfail_action,  unverified_sender_temp-
       fail_action, unknown_address_tempfail_action, and unknown_helo_hostname_tempfail_action.

       This feature is available in Postfix 2.6 and later.

relay_clientcerts (default: empty)
       List of tables with remote SMTP client-certificate fingerprints or public key fingerprints
       (Postfix 2.9 and later) for which the Postfix SMTP server will allow access with the  per-
       mit_tls_clientcerts  feature.   The  fingerprint  digest algorithm is configurable via the
       smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to Postfix version 2.5).

       Postfix lookup tables are in the form of (key, value) pairs.  Since we only need the  key,
       the   value   can   be	chosen	 freely,   e.g.    the	 name	of   the  user	or  host:
       D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80 lutzpc.at.home

       Example:

       relay_clientcerts = hash:/etc/postfix/relay_clientcerts

       For more fine-grained control, use check_ccert_access to select an  appropriate	access(5)
       policy for each client.	See RESTRICTION_CLASS_README.

       Note:  Postfix  2.9.0&ndash;2.9.5  computed the public key fingerprint incorrectly. To use
       public-key fingerprints, upgrade to Postfix 2.9.6 or later.

       This feature is available with Postfix version 2.2.

relay_destination_concurrency_limit (default: $default_destination_concurrency_limit)
       The maximal number of parallel deliveries to the same destination via  the  relay  message
       delivery  transport.  This  limit  is  enforced by the queue manager. The message delivery
       transport name is the first field in the entry in the master.cf file.

       This feature is available in Postfix 2.0 and later.

relay_destination_recipient_limit (default: $default_destination_recipient_limit)
       The maximal number of recipients per message for the  relay  message  delivery  transport.
       This  limit  is	enforced by the queue manager. The message delivery transport name is the
       first field in the entry in the master.cf file.

       Setting this parameter to a value of 1 changes the  meaning  of	relay_destination_concur-
       rency_limit from concurrency per domain into concurrency per recipient.

       This feature is available in Postfix 2.0 and later.

relay_domains (default: $mydestination)
       What  destination  domains (and subdomains thereof) this system will relay mail to. Subdo-
       main matching is  controlled  with  the	parent_domain_matches_subdomains  parameter.  For
       details	about  how  the  relay_domains	value  is  used,  see the description of the per-
       mit_auth_destination and reject_unauth_destination SMTP recipient restrictions.

       Domains that match $relay_domains are delivered with the  $relay_transport  mail  delivery
       transport.  The	SMTP  server validates recipient addresses with $relay_recipient_maps and
       rejects non-existent  recipients.  See  also  the  relay  domains  address  class  in  the
       ADDRESS_CLASS_README file.

       Note:  Postfix  will  not  automatically forward mail for domains that list this system as
       their primary or backup MX host. See the permit_mx_backup restriction in  the  postconf(5)
       manual page.

       Specify	a  list  of  host  or  domain names, "/file/name" patterns or "type:table" lookup
       tables, separated by commas and/or whitespace.  Continue long lines by starting	the  next
       line  with  whitespace. A "/file/name" pattern is replaced by its contents; a "type:table"
       lookup table is matched when a (parent) domain appears as lookup key.  Specify  "!pattern"
       to  exclude  a  domain  from the list. The form "!/file/name" is supported only in Postfix
       version 2.4 and later.

relay_domains_reject_code (default: 554)
       The numerical Postfix SMTP server response code when a client request is rejected  by  the
       reject_unauth_destination recipient restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

relay_recipient_maps (default: empty)
       Optional  lookup tables with all valid addresses in the domains that match $relay_domains.
       Specify @domain as a wild-card for domains that have no valid recipient list, and become a
       source  of  backscatter	mail:  Postfix	accepts spam for non-existent recipients and then
       floods  innocent  people  with  undeliverable  mail.   Technically,  tables  listed   with
       $relay_recipient_maps  are used as lists: Postfix needs to know only if a lookup string is
       found or not, but it does not use the result from table lookup.

       If this parameter is non-empty, then the Postfix SMTP server will reject mail  to  unknown
       relay users. This feature is off by default.

       See also the relay domains address class in the ADDRESS_CLASS_README file.

       Example:

       relay_recipient_maps = hash:/etc/postfix/relay_recipients

       This feature is available in Postfix 2.0 and later.

relay_transport (default: relay)
       The  default  mail  delivery  transport	and  next-hop  destination for remote delivery to
       domains listed with $relay_domains. In order of decreasing precedence, the nexthop  desti-
       nation  is  taken  from $relay_transport, $sender_dependent_relayhost_maps, $relayhost, or
       from the recipient domain. This information can be overruled with the transport(5) table.

       Specify a string of the form transport:nexthop, where transport is  the	name  of  a  mail
       delivery transport defined in master.cf.  The :nexthop destination is optional; its syntax
       is documented in the manual page of the corresponding delivery agent.

       See also the relay domains address class in the ADDRESS_CLASS_README file.

       This feature is available in Postfix 2.0 and later.

relayhost (default: empty)
       The next-hop destination of non-local  mail;  overrides	non-local  domains  in	recipient
       addresses.   This   information	 is   overruled   with	 relay_transport,   sender_depen-
       dent_default_transport_maps, default_transport, sender_dependent_relayhost_maps	and  with
       the transport(5) table.

       On  an  intranet,  specify the organizational domain name. If your internal DNS uses no MX
       records, specify the name of the intranet gateway host instead.

       In the case of SMTP, specify a  domain  name,  hostname,  hostname:port,  [hostname]:port,
       [hostaddress] or [hostaddress]:port. The form [hostname] turns off MX lookups.

       If you're connected via UUCP, see the UUCP_README file for useful information.

       Examples:

       relayhost = $mydomain
       relayhost = [gateway.example.com]
       relayhost = uucphost
       relayhost = [an.ip.add.ress]

relocated_maps (default: empty)
       Optional  lookup  tables  with new contact information for users or domains that no longer
       exist.  The table format and lookups are documented in relocated(5).

       If you use this feature, run "postmap /etc/postfix/relocated" to build the  necessary  DBM
       or DB file after change, then "postfix reload" to make the changes visible.

       Examples:

       relocated_maps = dbm:/etc/postfix/relocated
       relocated_maps = hash:/etc/postfix/relocated

remote_header_rewrite_domain (default: empty)
       Don't  rewrite  message	headers  from remote clients at all when this parameter is empty;
       otherwise, rewrite message headers and append the  specified  domain  name  to  incomplete
       addresses.   The local_header_rewrite_clients parameter controls what clients Postfix con-
       siders local.

       Examples:

       The safe setting: append "domain.invalid" to incomplete header addresses from remote  SMTP
       clients, so that those addresses cannot be confused with local addresses.

	   remote_header_rewrite_domain = domain.invalid

       The default, purist, setting: don't rewrite headers from remote clients at all.

	   remote_header_rewrite_domain =

require_home_directory (default: no)
       Require	that  a  local(8)  recipient's	home  directory  exists  before  mail delivery is
       attempted. By default this test is disabled.  It  can  be  useful  for  environments  that
       import  home  directories  to  the  mail  server (IMPORTING HOME DIRECTORIES IS NOT RECOM-
       MENDED).

reset_owner_alias (default: no)
       Reset the local(8) delivery agent's idea of the	owner-alias  attribute,  when  delivering
       mail to a child alias that does not have its own owner alias.

       This  feature  is  available  in  Postfix  2.8 and later. With older Postfix releases, the
       behavior is as if this parameter is set to "yes".

       As documented in aliases(5), when an alias name has a companion	alias  named  owner-name,
       delivery errors will be reported to the owner alias instead of the sender. This configura-
       tion is recommended for mailing lists.

       A less known property of the owner alias is that it  also  forces  the  local(8)  delivery
       agent  to  write  local	and  remote  addresses	from alias expansion to a new queue file,
       instead of attempting to deliver mail to local addresses as soon as they come out of alias
       expansion.

       Writing	local  addresses  from alias expansion to a new queue file allows for robust han-
       dling of temporary delivery errors: errors with one local member have no effect on  deliv-
       eries  to  other  members  of the list.	On the other hand, delivery to local addresses as
       soon as they come out of alias expansion is fragile: a  temporary  error  with  one  local
       address	from  alias expansion will cause the entire alias to be expanded repeatedly until
       the error goes away, or until the message expires in the queue.	In that case,  a  problem
       with one list member results in multiple message deliveries to other list members.

       The  default behavior of Postfix 2.8 and later is to keep the owner-alias attribute of the
       parent alias, when delivering mail to a child alias that  does  not  have  its  own  owner
       alias.  Then,  local  addresses from that child alias will be written to a new queue file,
       and a temporary error with one local address will not affect  delivery  to  other  mailing
       list members.

       Unfortunately, older Postfix releases reset the owner-alias attribute when delivering mail
       to a child alias that does not have its own owner alias.  The local(8) delivery agent then
       attempts to deliver local addresses as soon as they come out of child alias expansion.  If
       delivery to any address from child alias expansion fails with a temporary error condition,
       the  entire  mailing  list may be expanded repeatedly until the mail expires in the queue,
       resulting in multiple deliveries of the same message to mailing list members.

resolve_dequoted_address (default: yes)
       Resolve a recipient address safely instead of correctly, by looking inside quotes.

       By default, the Postfix address resolver does not quote the address localpart as  per  RFC
       822,  so  that additional @ or % or !  operators remain visible. This behavior is safe but
       it is also technically incorrect.

       If you specify "resolve_dequoted_address = no", then the Postfix resolver  will	not  know
       about  additional  @ etc. operators in the address localpart. This opens opportunities for
       obscure mail relay attacks with user@domain@domain addresses when Postfix provides  backup
       MX service for Sendmail systems.

resolve_null_domain (default: no)
       Resolve	an  address that ends in the "@" null domain as if the local hostname were speci-
       fied, instead of rejecting the address as invalid.

       This feature is available in Postfix 2.1 and later.  Earlier versions always  resolve  the
       null domain as the local hostname.

       The  Postfix SMTP server uses this feature to reject mail from or to addresses that end in
       the "@" null domain, and from addresses that rewrite into a form that ends in the "@" null
       domain.

resolve_numeric_domain (default: no)
       Resolve	"user@ipaddress"  as  "user@[ipaddress]",  instead  of	rejecting  the address as
       invalid.

       This feature is available in Postfix 2.3 and later.

rewrite_service_name (default: rewrite)
       The name of the address rewriting service. This service	rewrites  addresses  to  standard
       form and resolves them to a (delivery method, next-hop host, recipient) triple.

       This feature is available in Postfix 2.0 and later.

sample_directory (default: /etc/postfix)
       The name of the directory with example Postfix configuration files.  Starting with Postfix
       2.1, these files have been replaced with the postconf(5) manual page.

send_cyrus_sasl_authzid (default: no)
       When authenticating to a remote SMTP or LMTP server with the default setting "no", send no
       SASL  authoriZation  ID (authzid); send only the SASL authentiCation ID (authcid) plus the
       authcid's password.

       The non-default setting "yes" enables the  behavior  of	older  Postfix	versions.   These
       always  send a SASL authzid that is equal to the SASL authcid, but this causes inter-oper-
       ability problems with some SMTP servers.

       This feature is available in Postfix 2.4.4 and later.

sender_based_routing (default: no)
       This parameter should not be used. It was replaced by  sender_dependent_relayhost_maps  in
       Postfix version 2.3.

sender_bcc_maps (default: empty)
       Optional  BCC  (blind  carbon-copy) address lookup tables, indexed by sender address.  The
       BCC address (multiple results are not supported) is added when mail enters from outside of
       Postfix.

       This feature is available in Postfix 2.1 and later.

       The table search order is as follows:

       o      Look  up	the  "user+extension@domain.tld"  address  including the optional address
	      extension.

       o      Look up the "user@domain.tld" address without the optional address extension.

       o      Look up the "user+extension" address local part when the sender domain equals $myo-
	      rigin, $mydestination, $inet_interfaces or $proxy_interfaces.

       o      Look  up	the  "user"  address  local part when the sender domain equals $myorigin,
	      $mydestination, $inet_interfaces or $proxy_interfaces.

       o      Look up the "@domain.tld" part.

       Specify the types and names of databases to use.  After change,	run  "postmap  /etc/post-
       fix/sender_bcc".

       Note:  with  Postfix  2.3  and  later the BCC address is added as if it was specified with
       NOTIFY=NONE. The sender will not be notified when the BCC  address  is  undeliverable,  as
       long as all down-stream software implements RFC 3461.

       Note:  with  Postfix  2.2  and earlier the sender will be notified when the BCC address is
       undeliverable.

       Note: automatic BCC recipients are produced only for new mail.	To  avoid  mailer  loops,
       automatic  BCC  recipients  are	not  generated after Postfix forwards mail internally, or
       after Postfix generates mail itself.

       Example:

       sender_bcc_maps = hash:/etc/postfix/sender_bcc

sender_canonical_classes (default: envelope_sender, header_sender)
       What  addresses	are  subject  to  sender_canonical_maps  address  mapping.   By  default,
       sender_canonical_maps  address  mapping	is  applied  to envelope sender addresses, and to
       header sender addresses.

       Specify one or more of: envelope_sender, header_sender

       This feature is available in Postfix 2.2 and later.

sender_canonical_maps (default: empty)
       Optional address mapping lookup tables for envelope and header sender addresses.  The  ta-
       ble format and lookups are documented in canonical(5).

       Example:    you	  want	  to   rewrite	 the   SENDER	address   "user@ugly.domain"   to
       "user@pretty.domain", while still being	able  to  send	mail  to  the  RECIPIENT  address
       "user@ugly.domain".

       Note: $sender_canonical_maps is processed before $canonical_maps.

       Example:

       sender_canonical_maps = hash:/etc/postfix/sender_canonical

sender_dependent_default_transport_maps (default: empty)
       A sender-dependent override for the global default_transport parameter setting. The tables
       are searched by the envelope sender address and @domain. A lookup result of  DUNNO  termi-
       nates  the search without overriding the global default_transport parameter setting.  This
       information is overruled with the transport(5) table.

       Note: this overrides default_transport, not transport_maps,  and  therefore  the  expected
       syntax is that of default_transport, not the syntax of transport_maps.  Specifically, this
       does not support the transport_maps syntax for null transport, null nexthop, or null email
       addresses.

       For  safety  reasons, this feature does not allow $number substitutions in regular expres-
       sion maps.

       This feature is available in Postfix 2.7 and later.

sender_dependent_relayhost_maps (default: empty)
       A sender-dependent override for the global relayhost parameter  setting.  The  tables  are
       searched  by  the envelope sender address and @domain. A lookup result of DUNNO terminates
       the search without overriding the global relayhost  parameter  setting  (Postfix  2.6  and
       later).	  This	  information	 is   overruled   with	 relay_transport,   sender_depen-
       dent_default_transport_maps, default_transport and with the transport(5) table.

       For safety reasons, this feature does not allow $number substitutions in  regular  expres-
       sion maps.

       This feature is available in Postfix 2.3 and later.

sendmail_fix_line_endings (default: always)
       Controls  how  the  Postfix  sendmail  command  converts  email	message line endings from
       <CR><LF> into UNIX format (<LF>).

       always Always convert message lines ending in <CR><LF>. This setting is the  default  with
	      Postfix 2.9 and later.

       strict Convert  message	lines  ending  in  <CR><LF>  only if the first input line ends in
	      <CR><LF>. This setting is backwards-compatible with Postfix 2.8 and earlier.

       never  Never convert message lines ending in <CR><LF>. This setting exists  for	complete-
	      ness only.

       This feature is available in Postfix 2.9 and later.

sendmail_path (default: see postconf -d output)
       A  Sendmail  compatibility  feature that specifies the location of the Postfix sendmail(1)
       command. This command can be used to submit mail into the Postfix queue.

service_throttle_time (default: 60s)
       How long the Postfix master(8) waits before forking a server that appears to  be  malfunc-
       tioning.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

setgid_group (default: postdrop)
       The group ownership of set-gid Postfix commands and of group-writable Postfix directories.
       When  this  parameter  value is changed you need to re-run "postfix set-permissions" (with
       Postfix version 2.0 and earlier: "/etc/postfix/post-install set-permissions".

show_user_unknown_table_name (default: yes)
       Display the name of the recipient table in the "User unknown" responses.  The extra detail
       makes trouble shooting easier but also reveals information that is nobody elses business.

       This feature is available in Postfix 2.0 and later.

showq_service_name (default: showq)
       The name of the showq(8) service. This service produces mail queue status reports.

       This feature is available in Postfix 2.0 and later.

smtp_address_preference (default: any)
       The  address  type  ("ipv6", "ipv4" or "any") that the Postfix SMTP client will try first,
       when a destination has IPv6 and IPv4 addresses with equal MX preference. This feature  has
       no  effect unless the inet_protocols setting enables both IPv4 and IPv6.  With Postfix 2.8
       the default is "ipv6".

       Notes for mail delivery between sites that have both IPv4 and IPv6 connectivity:

       o      The setting "smtp_address_preference = ipv6" is unsafe.  It  can	fail  to  deliver
	      mail  when  there  is  an  outage that affects IPv6, while the destination is still
	      reachable over IPv4.

       o      The setting "smtp_address_preference = any" is safe. With this, mail  will  eventu-
	      ally  be delivered even if there is an outage that affects IPv6 or IPv4, as long as
	      it does not affect both.

       This feature is available in Postfix 2.8 and later.

smtp_always_send_ehlo (default: yes)
       Always send EHLO at the start of an SMTP session.

       With "smtp_always_send_ehlo = no", the Postfix SMTP client sends EHLO only when	the  word
       "ESMTP"	appears  in  the  server  greeting banner (example: 220 spike.porcupine.org ESMTP
       Postfix).

smtp_bind_address (default: empty)
       An optional numerical network address that the Postfix SMTP client  should  bind  to  when
       making an IPv4 connection.

       This  can be specified in the main.cf file for all SMTP clients, or it can be specified in
       the master.cf file for a specific client, for example:

	   /etc/postfix/master.cf:
	       smtp ... smtp -o smtp_bind_address=11.22.33.44

       Note 1: when inet_interfaces specifies no more than one IPv4 address, and that address  is
       a  non-loopback address, it is automatically used as the smtp_bind_address.  This supports
       virtual IP hosting, but can be a problem on multi-homed firewalls. See the inet_interfaces
       documentation for more detail.

       Note 2: address information may be enclosed inside [], but this form is not required here.

smtp_bind_address6 (default: empty)
       An  optional  numerical	network  address that the Postfix SMTP client should bind to when
       making an IPv6 connection.

       This feature is available in Postfix 2.2 and later.

       This can be specified in the main.cf file for all SMTP clients, or it can be specified  in
       the master.cf file for a specific client, for example:

	   /etc/postfix/master.cf:
	       smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8

       Note  1: when inet_interfaces specifies no more than one IPv6 address, and that address is
       a non-loopback address, it is automatically used as the smtp_bind_address6.  This supports
       virtual IP hosting, but can be a problem on multi-homed firewalls. See the inet_interfaces
       documentation for more detail.

       Note 2: address information may be enclosed inside [], but this form  is  not  recommended
       here.

smtp_body_checks (default: empty)
       Restricted  body_checks(5)  tables for the Postfix SMTP client.	These tables are searched
       while mail is being delivered.  Actions that change the delivery time or  destination  are
       not available.

       This feature is available in Postfix 2.5 and later.

smtp_cname_overrides_servername (default: version dependent)
       Allow  DNS  CNAME records to override the servername that the Postfix SMTP client uses for
       logging, SASL password lookup, TLS policy decisions, or TLS certificate verification.  The
       value  "no"  hardens Postfix smtp_tls_per_site hostname-based policies against false host-
       name information in DNS CNAME records, and makes SASL  password	file  lookups  more  pre-
       dictable. This is the default setting as of Postfix 2.3.

       This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)
       The Postfix SMTP client time limit for completing a TCP connection, or zero (use the oper-
       ating system built-in time limit).

       When no connection can be made within the deadline, the Postfix SMTP client tries the next
       address on the mail exchanger list. Specify 0 to disable the time limit (i.e. use whatever
       timeout is implemented by the operating system).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_connection_cache_destinations (default: empty)
       Permanently enable SMTP connection caching for the specified destinations.  With SMTP con-
       nection caching, a connection is not closed immediately after completion of a mail  trans-
       action.	 Instead, the connection is kept open for up to $smtp_connection_cache_time_limit
       seconds.  This allows connections to be reused for other deliveries, and can improve  mail
       delivery performance.

       Specify a comma or white space separated list of destinations or pseudo-destinations:

       o      if  mail	is  sent  without  a relay host: a domain name (the right-hand side of an
	      email address, without the [] around a numeric IP address),

       o      if mail is sent via a relay host: a relay host name (without [] or non-default  TCP
	      port), as specified in main.cf or in the transport map,

       o      if mail is sent via a UNIX-domain socket: a pathname (without the unix: prefix),

       o      a /file/name with domain names and/or relay host names as defined above,

       o      a  "type:table"  with  domain  names and/or relay host names on the left-hand side.
	      The right-hand side result from "type:table" lookups is ignored.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_on_demand (default: yes)
       Temporarily enable SMTP connection caching while a destination has a high volume  of  mail
       in the active queue.  With SMTP connection caching, a connection is not closed immediately
       after completion of a mail transaction.	Instead, the connection is kept open  for  up  to
       $smtp_connection_cache_time_limit seconds.  This allows connections to be reused for other
       deliveries, and can improve mail delivery performance.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_reuse_limit (default: 10)
       When SMTP connection caching is enabled, the number of times that an SMTP session  may  be
       reused before it is closed.

       This  feature  is available in Postfix 2.2. In Postfix 2.3 it is replaced by $smtp_connec-
       tion_reuse_time_limit.

smtp_connection_cache_time_limit (default: 2s)
       When SMTP connection caching is enabled, the amount of time that  an  unused  SMTP  client
       socket  is kept open before it is closed.  Do not specify larger values without permission
       from the remote sites.

       This feature is available in Postfix 2.2 and later.

smtp_connection_reuse_time_limit (default: 300s)
       The amount of time during which Postfix will use an SMTP connection repeatedly.	The timer
       starts  when  the connection is initiated (i.e. it includes the connect, greeting and helo
       latency, in addition to the latencies of subsequent mail delivery transactions).

       This feature addresses a performance stability problem  with  remote  SMTP  servers.  This
       problem is not specific to Postfix: it can happen when any MTA sends large amounts of SMTP
       email to a site that has multiple MX hosts.

       The problem starts when one of a set of MX hosts  becomes  slower  than	the  rest.   Even
       though  SMTP clients connect to fast and slow MX hosts with equal probability, the slow MX
       host ends up with more simultaneous inbound connections than the faster MX hosts,  because
       the slow MX host needs more time to serve each client request.

       The  slow  MX  host becomes a connection attractor.  If one MX host becomes N times slower
       than the rest, it dominates mail delivery latency unless there are more	than  N  fast  MX
       hosts  to  counter  the	effect. And if the number of MX hosts is smaller than N, the mail
       delivery latency becomes effectively that of the slowest MX host divided by the total num-
       ber of MX hosts.

       The  solution  uses connection caching in a way that differs from Postfix version 2.2.  By
       limiting the amount of time during which a connection can be used repeatedly  (instead  of
       limiting  the  number of deliveries over that connection), Postfix not only restores fair-
       ness in the distribution of simultaneous connections across a set of  MX  hosts,  it  also
       favors deliveries over connections that perform well, which is exactly what we want.

       The default reuse time limit, 300s, is comparable to the various smtp transaction timeouts
       which are fair estimates of maximum excess latency for a slow delivery.	Note  that  hosts
       may  accept  thousands  of messages over a single connection within the default connection
       reuse time limit. This number is much larger than the default Postfix version 2.2 limit of
       10  messages  per  cached  connection.  It may prove necessary to lower the limit to avoid
       interoperability issues with MTAs that exhibit bugs when many messages are delivered via a
       single  connection.  A lower reuse time limit risks losing the benefit of connection reuse
       when the average connection and mail delivery latency exceeds the reuse time limit.

       This feature is available in Postfix 2.3 and later.

smtp_data_done_timeout (default: 600s)
       The Postfix SMTP client time limit for sending the SMTP ".", and for receiving the  remote
       SMTP server response.

       When no response is received within the deadline, a warning is logged that the mail may be
       delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_data_init_timeout (default: 120s)
       The  Postfix  SMTP  client time limit for sending the SMTP DATA command, and for receiving
       the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_data_xfer_timeout (default: 180s)
       The Postfix SMTP client time limit for sending the SMTP message content.  When the connec-
       tion makes no progress for more than  $smtp_data_xfer_timeout  seconds  the  Postfix  SMTP
       client terminates the transfer.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

smtp_defer_if_no_mx_address_found (default: no)
       Defer mail delivery when no MX record resolves to an IP address.

       The default (no) is to return the mail as undeliverable. With older Postfix  versions  the
       default	was to keep trying to deliver the mail until someone fixed the MX record or until
       the mail was too old.

       Note: the Postfix SMTP client always ignores MX records with  equal  or	worse  preference
       than the local MTA itself.

       This feature is available in Postfix 2.1 and later.

smtp_destination_concurrency_limit (default: $default_destination_concurrency_limit)
       The  maximal  number  of  parallel deliveries to the same destination via the smtp message
       delivery transport. This limit is enforced by the  queue  manager.  The	message  delivery
       transport name is the first field in the entry in the master.cf file.

smtp_destination_recipient_limit (default: $default_destination_recipient_limit)
       The maximal number of recipients per message for the smtp message delivery transport. This
       limit is enforced by the queue manager. The message delivery transport name is  the  first
       field in the entry in the master.cf file.

       Setting	this  parameter  to  a value of 1 changes the meaning of smtp_destination_concur-
       rency_limit from concurrency per domain into concurrency per recipient.

smtp_discard_ehlo_keyword_address_maps (default: empty)
       Lookup tables, indexed by the remote SMTP server address, with case insensitive	lists  of
       EHLO  keywords (pipelining, starttls, auth, etc.) that the Postfix SMTP client will ignore
       in the EHLO response  from  a  remote  SMTP  server.  See  smtp_discard_ehlo_keywords  for
       details. The table is not indexed by hostname for consistency with smtpd_discard_ehlo_key-
       word_address_maps.

       This feature is available in Postfix 2.2 and later.

smtp_discard_ehlo_keywords (default: empty)
       A case insensitive list of EHLO keywords (pipelining, starttls, auth, etc.) that the Post-
       fix SMTP client will ignore in the EHLO response from a remote SMTP server.

       This feature is available in Postfix 2.2 and later.

       Notes:

       o      Specify the silent-discard pseudo keyword to prevent this action from being logged.

       o      Use  the	smtp_discard_ehlo_keyword_address_maps	feature  to discard EHLO keywords
	      selectively.

smtp_dns_resolver_options (default: empty)
       DNS Resolver options for the Postfix SMTP client.  Specify zero or more of  the	following
       options,  separated by comma or whitespace.  Option names are case-sensitive. Some options
       refer to domain names that are specified in the file /etc/resolv.conf or equivalent.

       res_defnames
	      Append the current domain name to single-component names (those that do not contain
	      a  "." character). This can produce incorrect results, and is the hard-coded behav-
	      ior prior to Postfix 2.8.

       res_dnsrch
	      Search for host names in the current domain and in parent domains. This can produce
	      incorrect results and is therefore not recommended.

       This feature is available in Postfix 2.8 and later.

smtp_enforce_tls (default: no)
       Enforcement mode: require that remote SMTP servers use TLS encryption, and never send mail
       in the clear.  This also requires that the remote SMTP server hostname matches the  infor-
       mation  in  the remote server certificate, and that the remote SMTP server certificate was
       issued by a CA that is trusted by the Postfix SMTP client. If the certificate doesn't ver-
       ify or the hostname doesn't match, delivery is deferred and mail stays in the queue.

       The server hostname is matched against all names provided as dNSNames in the SubjectAlter-
       nativeName.  If no dNSNames are specified, the CommonName is checked.  The behavior may be
       changed with the smtp_tls_enforce_peername option.

       This  option  is  useful  only  if  you	are definitely sure that you will only connect to
       servers that support RFC 2487 _and_ that provide valid server certificates.   Typical  use
       is for clients that send all their email to a dedicated mailhub.

       This  feature  is  available  in  Postfix  2.2  and  later. With Postfix 2.3 and later use
       smtp_tls_security_level instead.

smtp_fallback_relay (default: $fallback_relay)
       Optional list of relay hosts for SMTP  destinations  that  can't  be  found  or	that  are
       unreachable. With Postfix 2.2 and earlier this parameter is called fallback_relay.

       By  default,  mail is returned to the sender when a destination is not found, and delivery
       is deferred when a destination is unreachable.

       With bulk email deliveries, it can be beneficial to run the fallback relay MTA on the same
       host,  so  that	it  can  reuse the sender IP address.  This speeds up deliveries that are
       delayed by IP-based reputation systems (greylist, etc.).

       The fallback relays  must  be  SMTP  destinations.  Specify  a  domain,	host,  host:port,
       [host]:port,  [address]	or  [address]:port; the form [host] turns off MX lookups.  If you
       specify multiple SMTP destinations, Postfix will try them in the specified order.

       To prevent mailer loops between MX hosts and fall-back  hosts,  Postfix	version  2.2  and
       later  will  not use the fallback relays for destinations that it is MX host for (assuming
       DNS lookup is turned on).

smtp_generic_maps (default: empty)
       Optional lookup tables that perform address rewriting in the Postfix  SMTP  client,  typi-
       cally to transform a locally valid address into a globally valid address when sending mail
       across the Internet.  This is needed when the local machine does not have its own Internet
       domain name, but uses something like localdomain.local instead.

       The  table  format  and	lookups  are  documented in generic(5); examples are shown in the
       ADDRESS_REWRITING_README and STANDARD_CONFIGURATION_README documents.

       This feature is available in Postfix 2.2 and later.

smtp_header_checks (default: empty)
       Restricted header_checks(5) tables for the Postfix SMTP client.	These tables are searched
       while  mail  is being delivered.  Actions that change the delivery time or destination are
       not available.

       This feature is available in Postfix 2.5 and later.

smtp_helo_name (default: $myhostname)
       The hostname to send in the SMTP EHLO or HELO command.

       The default value is the machine hostname.  Specify a hostname or [ip.add.re.ss].

       This information can be specified in the main.cf file for all SMTP clients, or it  can  be
       specified in the master.cf file for a specific client, for example:

	   /etc/postfix/master.cf:
	       mysmtp ... smtp -o smtp_helo_name=foo.bar.com

       This feature is available in Postfix 2.0 and later.

smtp_helo_timeout (default: 300s)
       The Postfix SMTP client time limit for sending the HELO or EHLO command, and for receiving
       the initial remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_host_lookup (default: dns)
       What mechanisms the Postfix SMTP client uses to look up a host's IP address.  This parame-
       ter is ignored when DNS lookups are disabled (see: disable_dns_lookups).

       Specify one of the following:

       dns    Hosts can be found in the DNS (preferred).

       native Use the native naming service only (nsswitch.conf, or equivalent mechanism).

       dns, native
	      Use the native service for hosts not found in the DNS.

       This feature is available in Postfix 2.1 and later.

smtp_line_length_limit (default: 998)
       The maximal length of message header and body lines that Postfix will send via SMTP.  This
       limit  does  not include the <CR><LF> at the end of each line.  Longer lines are broken by
       inserting "<CR><LF><SPACE>", to minimize the damage to MIME formatted mail.

       The Postfix limit of 998 characters not including <CR><LF> is  consistent  with	the  SMTP
       limit  of  1000 characters including <CR><LF>.  The Postfix limit was 990 with Postfix 2.8
       and earlier.

smtp_mail_timeout (default: 300s)
       The Postfix SMTP client time limit for sending the MAIL FROM command,  and  for	receiving
       the remote SMTP server response.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

smtp_mime_header_checks (default: empty)
       Restricted mime_header_checks(5) tables for the Postfix	SMTP  client.  These  tables  are
       searched while mail is being delivered.	Actions that change the delivery time or destina-
       tion are not available.

       This feature is available in Postfix 2.5 and later.

smtp_mx_address_limit (default: 5)
       The maximal number of MX (mail exchanger) IP addresses that can result from  Postfix  SMTP
       client  mail  exchanger	lookups,  or  zero (no limit). Prior to Postfix version 2.3, this
       limit was disabled by default.

       This feature is available in Postfix 2.1 and later.

smtp_mx_session_limit (default: 2)
       The maximal number of SMTP sessions per delivery request before the  Postfix  SMTP  client
       gives  up  or  delivers	to  a  fall-back relay host, or zero (no limit). This restriction
       ignores sessions that fail to complete the SMTP initial handshake (Postfix version 2.2 and
       earlier)  or  that  fail  to  complete the EHLO and TLS handshake (Postfix version 2.3 and
       later).

       This feature is available in Postfix 2.1 and later.

smtp_nested_header_checks (default: empty)
       Restricted nested_header_checks(5) tables for the Postfix SMTP client.  These  tables  are
       searched while mail is being delivered.	Actions that change the delivery time or destina-
       tion are not available.

       This feature is available in Postfix 2.5 and later.

smtp_never_send_ehlo (default: no)
       Never send EHLO at the start of an SMTP session. See also the smtp_always_send_ehlo param-
       eter.

smtp_per_record_deadline (default: no)
       Change the behavior of the smtp_*_timeout time limits, from a time limit per read or write
       system call, to a time limit to send or receive a complete record (an SMTP  command  line,
       SMTP  response line, SMTP message content line, or TLS protocol message).  This limits the
       impact from hostile peers that trickle data one byte at a time.

       Note: when per-record deadlines are enabled, a short timeout may cause problems	with  TLS
       over very slow network connections.  The reasons are that a TLS protocol message can be up
       to 16 kbytes long (with TLSv1), and that an entire TLS protocol message must  be  sent  or
       received within the per-record deadline.

       This  feature  is  available  in  Postfix  2.9 and later. With older Postfix releases, the
       behavior is as if this parameter is set to "no".

smtp_pix_workaround_delay_time (default: 10s)
       How long the Postfix SMTP client pauses before sending ".<CR><LF>" in order to work around
       the PIX firewall "<CR><LF>.<CR><LF>" bug.

       Choosing  a  too  short time makes this workaround ineffective when sending large messages
       over slow network connections.

smtp_pix_workaround_maps (default: empty)
       Lookup tables, indexed by the remote SMTP server address, with per-destination workarounds
       for  CISCO  PIX	firewall bugs.	The table is not indexed by hostname for consistency with
       smtp_discard_ehlo_keyword_address_maps.

       This feature is available in Postfix 2.4 and later.

smtp_pix_workaround_threshold_time (default: 500s)
       How long a message must be queued before the Postfix SMTP client turns on the PIX firewall
       "<CR><LF>.<CR><LF>"  bug  workaround for delivery through firewalls with "smtp fixup" mode
       turned on.

       By default, the workaround is turned off for mail that is queued for less  than	500  sec-
       onds.  In  other  words,  the  workaround  is  normally	turned off for the first delivery
       attempt.

       Specify 0 to enable the PIX firewall "<CR><LF>.<CR><LF>" bug  workaround  upon  the  first
       delivery attempt.

smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf)
       A  list	that  specifies zero or more workarounds for CISCO PIX firewall bugs. These work-
       arounds are implemented by the Postfix SMTP client.  Workaround	names  are  separated  by
       comma  or  space,  and are case insensitive.  This parameter setting can be overruled with
       per-destination smtp_pix_workaround_maps settings.

       delay_dotcrlf
	      Insert a delay before sending ".<CR><LF>" after the end  of  the	message  content.
	      The  delay  is  subject  to  the	smtp_pix_workaround_delay_time and smtp_pix_work-
	      around_threshold_time parameter settings.

       disable_esmtp
	      Disable all extended SMTP commands: send HELO instead of EHLO.

       This feature is available in Postfix 2.4 and later. The	default  settings  are	backwards
       compatible with earlier Postfix versions.

smtp_quit_timeout (default: 300s)
       The  Postfix  SMTP  client  time limit for sending the QUIT command, and for receiving the
       remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_quote_rfc821_envelope (default: yes)
       Quote  addresses  in Postfix SMTP client MAIL FROM and RCPT TO commands as required by RFC
       5321. This includes putting quotes around an address localpart that ends in ".".

       The default is to comply with RFC 5321. If you have to send mail to a broken SMTP  server,
       configure a special SMTP client in master.cf:

	   /etc/postfix/master.cf:
	       broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no

       and  route mail for the destination in question to the "broken-smtp" message delivery with
       a transport(5) table.

       This feature is available in Postfix 2.1 and later.

smtp_randomize_addresses (default: yes)
       Randomize the order of equal-preference MX host addresses.  This is a performance  feature
       of the Postfix SMTP client.

smtp_rcpt_timeout (default: 300s)
       The Postfix SMTP client time limit for sending the SMTP RCPT TO command, and for receiving
       the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_reply_filter (default: empty)
       A  mechanism  to transform replies from remote SMTP servers one line at a time.	This is a
       last-resort tool to work around server replies that break inter-operability with the Post-
       fix SMTP client.  Other uses involve fault injection to test Postfix's handling of invalid
       responses.

       Notes:

       o      In the case of a multi-line reply, the Postfix SMTP client  uses	the  final  reply
	      line's numerical SMTP reply code and enhanced status code.

       o      The  numerical SMTP reply code (XYZ) takes precedence over the enhanced status code
	      (X.Y.Z).	When the enhanced status code initial digit differs from the  SMTP  reply
	      code  initial  digit,  or when no enhanced status code is present, the Postfix SMTP
	      client uses a generic enhanced status code (X.0.0) instead.

       Specify the name of a "type:table" lookup table. The search string is a single SMTP  reply
       line  as  received  from  the  remote  SMTP  server, except that the trailing <CR><LF> are
       removed.  When the lookup succeeds, the result replaces the single SMTP reply line.

       Examples:

       /etc/postfix/main.cf:
	   smtp_reply_filter = pcre:/etc/postfix/reply_filter

       /etc/postfix/reply_filter:
	   # Transform garbage into "250-filler..." so that it looks like
	   # one line from a multi-line reply. It does not matter what we
	   # substitute here as long it has the right syntax.  The Postfix
	   # SMTP client will use the final line's numerical SMTP reply
	   # code and enhanced status code.
	   !/^([2-5][0-9][0-9]($|[- ]))/ 250-filler for garbage

       This feature is available in Postfix 2.7.

smtp_rset_timeout (default: 20s)
       The Postfix SMTP client time limit for sending the RSET command,  and  for  receiving  the
       remote  SMTP  server  response.	The SMTP client sends RSET in order to finish a recipient
       address probe, or to verify that a cached session is still usable.

       This feature is available in Postfix 2.1 and later.

smtp_sasl_auth_cache_name (default: empty)
       An optional table to prevent repeated SASL authentication failures with	the  same  remote
       SMTP  server  hostname,	username  and  password.  Each table (key, value) pair contains a
       server name, a username and password, and the full server response.  This  information  is
       stored  when a remote SMTP server rejects an authentication attempt with a 535 reply code.
       As long as the smtp_sasl_password_maps information does no change,  and	as  long  as  the
       smtp_sasl_auth_cache_name  information does not expire (see smtp_sasl_auth_cache_time) the
       Postfix SMTP client avoids SASL authentication attempts with the same server, username and
       password,    and    instead    bounces	or   defers   mail   as   controlled   with   the
       smtp_sasl_auth_soft_bounce configuration parameter.

       Use a per-destination delivery concurrency of 1	(for  example,	"smtp_destination_concur-
       rency_limit  =  1",  "relay_destination_concurrency_limit  = 1", etc.), otherwise multiple
       delivery agents may experience a login failure at the same time.

       The table must be accessed via the proxywrite service, i.e. the map name must  start  with
       "proxy:". The table should be stored under the directory specified with the data_directory
       parameter.

       This feature uses cryptographic hashing to protect plain-text passwords, and requires that
       Postfix is compiled with TLS support.

       Example:

       smtp_sasl_auth_cache_name = proxy:btree:/var/lib/postfix/sasl_auth_cache

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_cache_time (default: 90d)
       The maximal age of an smtp_sasl_auth_cache_name entry before it is removed.

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_enable (default: no)
       Enable  SASL  authentication  in  the  Postfix  SMTP client.  By default, the Postfix SMTP
       client uses no authentication.

       Example:

       smtp_sasl_auth_enable = yes

smtp_sasl_auth_soft_bounce (default: yes)
       When a remote SMTP server rejects a SASL authentication request with  a	535  reply  code,
       defer  mail  delivery  instead of returning mail as undeliverable. The latter behavior was
       hard-coded prior to Postfix version 2.5.

       Note: the setting "yes" overrides the global soft_bounce parameter, but the  setting  "no"
       does not.

       Example:

       # Default as of Postfix 2.5
       smtp_sasl_auth_soft_bounce = yes
       # The old hard-coded default
       smtp_sasl_auth_soft_bounce = no

       This feature is available in Postfix 2.5 and later.

smtp_sasl_mechanism_filter (default: empty)
       If  non-empty,  a  Postfix SMTP client filter for the remote SMTP server's list of offered
       SASL mechanisms.  Different client and server implementations may support different mecha-
       nism  lists;  by  default,  the	Postfix SMTP client will use the intersection of the two.
       smtp_sasl_mechanism_filter specifies an optional third mechanism list to intersect with.

       Specify mechanism names, "/file/name" patterns or "type:table" lookup tables.  The  right-
       hand  side  result  from  "type:table" lookups is ignored. Specify "!pattern" to exclude a
       mechanism name from the list. The form "!/file/name" is supported only in Postfix  version
       2.4 and later.

       This feature is available in Postfix 2.2 and later.

       Examples:

       smtp_sasl_mechanism_filter = plain, login
       smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
       smtp_sasl_mechanism_filter = !gssapi, !login, static:rest

smtp_sasl_password_maps (default: empty)
       Optional  Postfix  SMTP	client	lookup tables with one username:password entry per remote
       hostname or domain, or sender address when sender-dependent authentication is enabled.  If
       no  username:password  entry  is  found,  then the Postfix SMTP client will not attempt to
       authenticate to the remote host.

       The Postfix SMTP client opens the lookup table before going to chroot  jail,  so  you  can
       leave the password file in /etc/postfix.

smtp_sasl_path (default: empty)
       Implementation-specific	information  that  the	Postfix SMTP client passes through to the
       SASL plug-in implementation that is selected with smtp_sasl_type.  Typically  this  speci-
       fies the name of a configuration file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

smtp_sasl_security_options (default: noplaintext, noanonymous)
       Postfix	SMTP  client  SASL security options; as of Postfix 2.3 the list of available fea-
       tures depends on the SASL client implementation that is selected with smtp_sasl_type.

       The following security features are defined for the cyrus client SASL implementation:

       Specify zero or more of the following:

       noplaintext
	      Disallow methods that use plaintext passwords.

       noactive
	      Disallow methods subject to active (non-dictionary) attack.

       nodictionary
	      Disallow methods subject to passive (dictionary) attack.

       noanonymous
	      Disallow methods that allow anonymous authentication.

       mutual_auth
	      Only allow methods that provide mutual authentication (not available with SASL ver-
	      sion 1).

       Example:

       smtp_sasl_security_options = noplaintext

smtp_sasl_tls_security_options (default: $smtp_sasl_security_options)
       The  SASL  authentication  security  options  that  the	Postfix  SMTP client uses for TLS
       encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtp_sasl_tls_verified_security_options (default: $smtp_sasl_tls_security_options)
       The SASL authentication security options  that  the  Postfix  SMTP  client  uses  for  TLS
       encrypted SMTP sessions with a verified server certificate.

       When  mail  is  sent to the public MX host for the recipient's domain, server certificates
       are by default optional, and delivery proceeds even if certificate verification fails. For
       delivery via a submission service that requires SASL authentication, it may be appropriate
       to send plaintext passwords only when the connection to the server is  strongly	encrypted
       and the server identity is verified.

       The  smtp_sasl_tls_verified_security_options  parameter	makes  it possible to only enable
       plaintext mechanisms when a secure connection  to  the  server  is  available.  Submission
       servers	subject to this policy must either have verifiable certificates or offer suitable
       non-plaintext SASL mechanisms.

       This feature is available in Postfix 2.6 and later.

smtp_sasl_type (default: cyrus)
       The SASL plug-in type that the Postfix SMTP client should  use  for  authentication.   The
       available types are listed with the "postconf -A" command.

       This feature is available in Postfix 2.3 and later.

smtp_send_dummy_mail_auth (default: no)
       Whether	or  not to append the "AUTH=<>" option to the MAIL FROM command in SASL-authenti-
       cated SMTP sessions. The default is not to send this, to avoid problems with broken remote
       SMTP servers.  Before Postfix 2.9 the behavior is as if "smtp_send_dummy_mail_auth = yes".

       This feature is available in Postfix 2.9 and later.

smtp_send_xforward_command (default: no)
       Send  the  non-standard	XFORWARD  command  when  the  Postfix  SMTP  server EHLO response
       announces XFORWARD support.

       This allows a Postfix SMTP delivery agent, used for injecting mail into a content  filter,
       to forward the name, address, protocol and HELO name of the original client to the content
       filter and downstream queuing SMTP server. This	can  produce  more  useful  logging  than
       localhost[127.0.0.1] etc.

       This feature is available in Postfix 2.1 and later.

smtp_sender_dependent_authentication (default: no)
       Enable  sender-dependent authentication in the Postfix SMTP client; this is available only
       with SASL authentication, and disables SMTP connection caching to ensure  that  mail  from
       different senders will use the appropriate credentials.

       This feature is available in Postfix 2.3 and later.

smtp_skip_4xx_greeting (default: yes)
       Skip SMTP servers that greet with a 4XX status code (go away, try again later).

       By  default,  the  Postfix  SMTP  client  moves	on  the  next  mail  exchanger.   Specify
       "smtp_skip_4xx_greeting = no" if Postfix should defer delivery immediately.

       This feature is available in Postfix 2.0 and earlier.  Later Postfix versions always  skip
       remote SMTP servers that greet with a 4XX status code.

smtp_skip_5xx_greeting (default: yes)
       Skip  remote  SMTP  servers  that  greet with a 5XX status code (go away, do not try again
       later).

       By  default,  the  Postfix  SMTP  client  moves	on  the  next  mail  exchanger.   Specify
       "smtp_skip_5xx_greeting	=  no" if Postfix should bounce the mail immediately. The default
       setting is incorrect, but it is what a lot of people expect to happen.

smtp_skip_quit_response (default: yes)
       Do not wait for the response to the SMTP QUIT command.

smtp_starttls_timeout (default: 300s)
       Time limit for Postfix SMTP client write and read operations during TLS startup and  shut-
       down handshake procedures.

       This feature is available in Postfix 2.2 and later.

smtp_tls_CAfile (default: empty)
       A  file	containing  CA certificates of root CAs trusted to sign either remote SMTP server
       certificates or intermediate CA certificates.  These are loaded	into  memory  before  the
       smtp(8)	client	enters the chroot jail. If the number of trusted roots is large, consider
       using smtp_tls_CApath instead, but note that the latter directory must be present  in  the
       chroot  jail  if the smtp(8) client is chrooted. This file may also be used to augment the
       client certificate trust chain, but it is best to include all  the  required  certificates
       directly in $smtp_tls_cert_file.

       Specify	"smtp_tls_CAfile  =  /path/to/system_CA_file"  to  use	ONLY  the system-supplied
       default certificate authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending the system-supplied
       default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_CApath (default: empty)
       Directory  with PEM format certificate authority certificates that the Postfix SMTP client
       uses to verify a remote SMTP server certificate.  Don't forget  to  create  the	necessary
       "hash" links with, for example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".

       To  use	this  option in chroot mode, this directory (or a copy) must be inside the chroot
       jail.

       Specify "smtp_tls_CApath = /path/to/system_CA_directory" to use ONLY  the  system-supplied
       default certificate authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending the system-supplied
       default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtp_tls_block_early_mail_reply (default: no)
       Try  to	detect	a  mail  hijacking  attack  based  on  a   TLS	 protocol   vulnerability
       (CVE-2009-3555), where an attacker prepends malicious HELO, MAIL, RCPT, DATA commands to a
       Postfix SMTP client TLS session.  The attack would succeed with non-Postfix  SMTP  servers
       that  reply to the malicious HELO, MAIL, RCPT, DATA commands after negotiating the Postfix
       SMTP client TLS session.

       This feature is available in Postfix 2.7.

smtp_tls_cert_file (default: empty)
       File with the Postfix SMTP client RSA certificate in PEM format.  This file may also  con-
       tain  the  Postfix  SMTP  client private RSA key, and these may be the same as the Postfix
       SMTP server RSA certificate and key file.

       Do not configure client certificates unless you must present client  TLS  certificates  to
       one or more servers. Client certificates are not usually needed, and can cause problems in
       configurations that work well without them. The recommended setting is to let the defaults
       stand:

	   smtp_tls_cert_file =
	   smtp_tls_key_file =
	   smtp_tls_dcert_file =
	   smtp_tls_dkey_file =
	   smtp_tls_eccert_file =
	   smtp_tls_eckey_file =

       The best way to use the default settings is to comment out the above parameters in main.cf
       if present.

       To enable remote SMTP servers to verify the Postfix SMTP client certificate,  the  issuing
       CA certificates must be made available to the server. You should include the required cer-
       tificates in the client certificate file, the client certificate first, then  the  issuing
       CA(s) (bottom-up order).

       Example:  the  certificate  for "client.example.com" was issued by "intermediate CA" which
       itself has a certificate issued by "root  CA".	Create	the  client.pem  file  with  "cat
       client_cert.pem intermediate_CA.pem root_CA.pem > client.pem".

       If  you	also  want to verify remote SMTP server certificates issued by these CAs, you can
       add the CA certificates to the smtp_tls_CAfile, in which case it is not necessary to  have
       them in the smtp_tls_cert_file, smtp_tls_dcert_file or smtp_tls_eccert_file.

       A certificate supplied here must be usable as an SSL client certificate and hence pass the
       "openssl verify -purpose sslclient ..." test.

       Example:

       smtp_tls_cert_file = /etc/postfix/client.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_cipherlist (default: empty)
       Obsolete Postfix < 2.3 control for the Postfix SMTP client TLS cipher list. As  this  fea-
       ture  applies  to all TLS security levels, it is easy to create inter-operability problems
       by choosing a non-default cipher list. Do not use a non-default TLS cipher list	on  hosts
       that  deliver  email  to  the public Internet: you will be unable to send email to servers
       that only support the ciphers you exclude. Using a restricted  cipher  list  may  be  more
       appropriate  for  an  internal MTA, where one can exert some control over the TLS software
       and settings of the peer servers.

       Note: do not use "" quotes around the parameter value.

       This feature is available in Postfix version 2.2. It is not  used  with	Postfix  2.3  and
       later; use smtp_tls_mandatory_ciphers instead.

smtp_tls_ciphers (default: export)
       The  minimum TLS cipher grade that the Postfix SMTP client will use with opportunistic TLS
       encryption. Cipher types listed in smtp_tls_exclude_ciphers are	excluded  from	the  base
       definition of the selected cipher grade. The default value "export" ensures maximum inter-
       operability. Because encryption is optional, stronger controls are  not	appropriate,  and
       this setting SHOULD NOT be changed unless the change is essential.

       When  TLS  is mandatory the cipher grade is chosen via the smtp_tls_mandatory_ciphers con-
       figuration parameter, see there for syntax details. See smtp_tls_policy_maps for  informa-
       tion on how to configure ciphers on a per-destination basis.

       Example:
       smtp_tls_ciphers = export

       This feature is available in Postfix 2.6 and later. With earlier Postfix releases only the
       smtp_tls_mandatory_ciphers parameter is implemented, and  opportunistic	TLS  always  uses
       "export" or better (i.e. all) ciphers.

smtp_tls_dcert_file (default: empty)
       File  with the Postfix SMTP client DSA certificate in PEM format.  This file may also con-
       tain the Postfix SMTP client private DSA key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_dcert_file = /etc/postfix/client-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_dkey_file (default: $smtp_tls_dcert_file)
       File with the Postfix SMTP client DSA private key in PEM format.  This file  may  be  com-
       bined   with   the   Postfix   SMTP   client   DSA   certificate   file	 specified   with
       $smtp_tls_dcert_file.

       The private key must be accessible without a pass-phrase, i.e. it must not  be  encrypted.
       File  permissions  should grant read-only access to the system superuser account ("root"),
       and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtp_tls_eccert_file (default: empty)
       File with the Postfix SMTP client ECDSA certificate in PEM format.   This  file	may  also
       contain the Postfix SMTP client ECDSA private key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_eccert_file = /etc/postfix/ecdsa-ccert.pem

       This  feature  is  available in Postfix 2.6 and later, when Postfix is compiled and linked
       with OpenSSL 1.0.0 or later.

smtp_tls_eckey_file (default: $smtp_tls_eccert_file)
       File with the Postfix SMTP client ECDSA private key in PEM format.  This file may be  com-
       bined   with   the   Postfix   SMTP   client   ECDSA   certificate   file  specified  with
       $smtp_tls_eccert_file.

       The private key must be accessible without a pass-phrase, i.e. it must not  be  encrypted.
       File  permissions  should grant read-only access to the system superuser account ("root"),
       and no access to anyone else.

       This feature is available in Postfix 2.6 and later, when Postfix is  compiled  and  linked
       with OpenSSL 1.0.0 or later.

smtp_tls_enforce_peername (default: yes)
       With  mandatory	TLS  encryption, require that the remote SMTP server hostname matches the
       information in the remote SMTP server certificate.  As of RFC 2487  the	requirements  for
       hostname checking for MTA clients are not specified.

       This  option  can be set to "no" to disable strict peer name checking. This setting has no
       effect on sessions that are controlled via the smtp_tls_per_site table.

       Disabling the hostname verification can make sense in closed environment where special CAs
       are created.  If not used carefully, this option opens the danger of a "man-in-the-middle"
       attack (the CommonName of this attacker will be logged).

       This feature is available in Postfix 2.2  and  later.  With  Postfix  2.3  and  later  use
       smtp_tls_security_level instead.

smtp_tls_exclude_ciphers (default: empty)
       List of ciphers or cipher types to exclude from the Postfix SMTP client cipher list at all
       TLS security levels. This is not an OpenSSL cipherlist, it is a simple list  separated  by
       whitespace  and/or  commas. The elements are a single cipher, or one or more "+" separated
       cipher properties, in which case only ciphers matching all the properties are excluded.

       Examples (some of these will cause problems):

	   smtp_tls_exclude_ciphers = aNULL
	   smtp_tls_exclude_ciphers = MD5, DES
	   smtp_tls_exclude_ciphers = DES+MD5
	   smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
	   smtp_tls_exclude_ciphers = kEDH+aRSA

       The first setting, disables anonymous ciphers. The next setting disables ciphers that  use
       the  MD5  digest algorithm or the (single) DES encryption algorithm. The next setting dis-
       ables ciphers that use MD5 and DES together.  The next setting disables	the  two  ciphers
       "AES256-SHA"  and  "DES-CBC3-MD5".  The	last  setting disables ciphers that use "EDH" key
       exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtp_tls_fingerprint_cert_match (default: empty)
       List of acceptable remote SMTP server certificate fingerprints for the  "fingerprint"  TLS
       security  level	(smtp_tls_security_level = fingerprint). At this security level, certifi-
       cate authorities are not used, and certificate  expiration  times  are  ignored.  Instead,
       server  certificates are verified directly via their certificate fingerprint or public key
       fingerprint (Postfix 2.9 and later). The fingerprint is a message  digest  of  the  server
       certificate  (or  public  key).	The digest algorithm is selected via the smtp_tls_finger-
       print_digest parameter.

       When an smtp_tls_policy_maps table entry specifies the "fingerprint" security  level,  any
       "match"	attributes  in	that  entry specify the list of valid fingerprints for the corre-
       sponding destination. Multiple fingerprints can be combined with a "|" delimiter in a sin-
       gle match attribute, or multiple match attributes can be employed.

       Example: Certificate fingerprint verification with internal mailhub.  Two matching finger-
       prints are listed. The relayhost may be multiple physical hosts	behind	a  load-balancer,
       each  with its own private/public key and self-signed certificate. Alternatively, a single
       relayhost may be in the process of switching  from  one	set  of  private/public  keys  to
       another, and both keys are trusted just prior to the transition.

	   relayhost = [mailhub.example.com]
	   smtp_tls_security_level = fingerprint
	   smtp_tls_fingerprint_digest = md5
	   smtp_tls_fingerprint_cert_match =
	       3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
	       EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       Example: Certificate fingerprint verification with selected destinations.  As in the exam-
       ple above, we show two matching fingerprints:

	   /etc/postfix/main.cf:
	       smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
	       smtp_tls_fingerprint_digest = md5

	   /etc/postfix/tls_policy:
	       example.com     fingerprint
		   match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
		   match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.5 and later.

smtp_tls_fingerprint_digest (default: md5)
       The message digest algorithm used to construct  remote  SMTP  server  certificate  finger-
       prints.	At  the "fingerprint" TLS security level (smtp_tls_security_level = fingerprint),
       the server certificate is verified by directly matching its certificate fingerprint or its
       public  key  fingerprint (Postfix 2.9 and later). The fingerprint is the message digest of
       the server certificate (or its public key) using the selected  algorithm.  With	a  digest
       algorithm resistant to "second pre-image" attacks, it is not feasible to create a new pub-
       lic key and a matching certificate (or public/private key-pair) that has the same  finger-
       print.

       The  default algorithm is md5; this is consistent with the backwards compatible setting of
       the digest used to verify client certificates in the SMTP server.

       The best practice algorithm is now sha1. Recent advances in  hash  function  cryptanalysis
       have led to md5 being deprecated in favor of sha1.  However, as long as there are no known
       "second pre-image" attacks against md5, its use in this context can  still  be  considered
       safe.

       While  additional  digest  algorithms  are  often available with OpenSSL's libcrypto, only
       those used by libssl in SSL cipher suites are available to Postfix.  For  now  this  means
       just md5 or sha1.

       To  find the fingerprint of a specific certificate file, with a specific digest algorithm,
       run:

	   $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The text to the right of "=" sign is the desired fingerprint.  For example:

	   $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
	   SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       To extract the public key fingerprint from an X.509 certificate, you need to  extract  the
       public  key  from  the  certificate  and compute the appropriate digest of its DER (ASN.1)
       encoding. With OpenSSL the "-pubkey" option of the "x509" command extracts the public  key
       always  in  "PEM"  format. We pipe the result to another OpenSSL command that converts the
       key to DER and then to the "dgst" command to compute the fingerprint.

       The actual command to transform the key to DER format depends on the  version  of  OpenSSL
       used.  With  OpenSSL  1.0.0  and  later,  the  "pkey" command supports all key types. With
       OpenSSL 0.9.8 and earlier, the key type is always RSA (nobody uses DSA, and  EC	keys  are
       not fully supported by 0.9.8), so the "rsa" command is used.

	   # OpenSSL 1.0 with all certificates and SHA-1 fingerprints.
	   $ openssl x509 -in cert.pem -noout -pubkey |
	       openssl pkey -pubin -outform DER |
	       openssl dgst -sha1 -c
	   (stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58

	   # OpenSSL 0.9.8 with RSA certificates and MD5 fingerprints.
	   $ openssl x509 -in cert.pem -noout -pubkey |
	       openssl rsa -pubin -outform DER |
	       openssl dgst -md5 -c
	   (stdin)= f4:62:60:f6:12:8f:d5:8d:28:4d:13:a7:db:b2:ff:50

       The  Postfix SMTP server and client log the peer (leaf) certificate fingerprint and public
       key fingerprint when the TLS loglevel is 2 or higher.

       Note: Postfix 2.9.0&ndash;2.9.5 computed the public key fingerprint  incorrectly.  To  use
       public-key fingerprints, upgrade to Postfix 2.9.6 or later.

       This feature is available in Postfix 2.5 and later.

smtp_tls_key_file (default: $smtp_tls_cert_file)
       File  with  the	Postfix SMTP client RSA private key in PEM format.  This file may be com-
       bined   with   the   Postfix   SMTP   client   RSA   certificate   file	 specified   with
       $smtp_tls_cert_file.

       The  private  key must be accessible without a pass-phrase, i.e. it must not be encrypted.
       File permissions should grant read-only access to the system superuser  account	("root"),
       and no access to anyone else.

       Example:

       smtp_tls_key_file = $smtp_tls_cert_file

       This feature is available in Postfix 2.2 and later.

smtp_tls_loglevel (default: 0)
       Enable  additional  Postfix  SMTP client logging of TLS activity.  Each logging level also
       includes the information that is logged at a lower logging level.

	      0 Log only a summary message on TLS handshake  completion  &mdash;  no  logging  of
	      remote  SMTP  server certificate trust-chain verification errors if server certifi-
	      cate verification is not required.  With Postfix 2.8 and earlier,  disable  logging
	      of TLS activity.

	      1  Also log remote SMTP server trust-chain verification errors and peer certificate
	      summary information. With Postfix 2.8 and earlier, log TLS handshake  and  certifi-
	      cate information.

	      2 Also log levels during TLS negotiation.

	      3 Also log hexadecimal and ASCII dump of TLS negotiation process.

	      4 Also log hexadecimal and ASCII dump of complete transmission after STARTTLS.

       Do not use "smtp_tls_loglevel = 2" or higher except in case of problems. Use of loglevel 4
       is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtp_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP client  will	use  with  mandatory  TLS
       encryption.   The  default value "medium" is suitable for most destinations with which you
       may want to enforce TLS, and is beyond the reach of  today's  cryptanalytic  methods.  See
       smtp_tls_policy_maps  for  information  on  how	to configure ciphers on a per-destination
       basis.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or better OpenSSL ciphers.	This is the  default  for  oppor-
	      tunistic encryption. It is not recommended for mandatory encryption unless you must
	      enforce TLS with "crippled" peers. The underlying cipherlist is specified  via  the
	      tls_export_cipherlist configuration parameter, which you are strongly encouraged to
	      not change.

       low    Enable "LOW" grade or better OpenSSL ciphers.  This setting is only appropriate for
	      internal	 mail	servers.    The   underlying  cipherlist  is  specified  via  the
	      tls_low_cipherlist configuration parameter, which you are  strongly  encouraged  to
	      not change.

       medium Enable  "MEDIUM"	grade  or  better  OpenSSL ciphers.  The underlying cipherlist is
	      specified via the tls_medium_cipherlist  configuration  parameter,  which  you  are
	      strongly encouraged to not change.

       high   Enable only "HIGH" grade OpenSSL ciphers.  This setting may be appropriate when all
	      mandatory TLS destinations (e.g. when all mail is  routed  to  a	suitably  capable
	      relayhost)  support  at least one "HIGH" grade cipher. The underlying cipherlist is
	      specified via  the  tls_high_cipherlist  configuration  parameter,  which  you  are
	      strongly encouraged to not change.

       null   Enable  only  the  "NULL"  OpenSSL  ciphers,  these  provide authentication without
	      encryption.  This setting is only appropriate in the rare case that all servers are
	      prepared	to  use  NULL  ciphers (not normally enabled in TLS servers). A plausible
	      use-case is an LMTP server listening on a UNIX-domain socket that is configured  to
	      support	"NULL"	 ciphers.   The   underlying  cipherlist  is  specified  via  the
	      tls_null_cipherlist configuration parameter, which you are strongly  encouraged  to
	      not change.

       The  underlying	cipherlists  for  grades other than "null" include anonymous ciphers, but
       these are automatically filtered out if the Postfix SMTP client is  configured  to  verify
       server certificates.  You are very unlikely to need to take any steps to exclude anonymous
       ciphers, they are excluded automatically as necessary.	If  you  must  exclude	anonymous
       ciphers	at  the "may" or "encrypt" security levels, when the Postfix SMTP client does not
       need or use peer certificates, set "smtp_tls_exclude_ciphers = aNULL". To  exclude  anony-
       mous ciphers only when TLS is enforced, set "smtp_tls_mandatory_exclude_ciphers = aNULL".

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_exclude_ciphers (default: empty)
       Additional  list of ciphers or cipher types to exclude from the Postfix SMTP client cipher
       list at mandatory TLS security levels. This list  works	in  addition  to  the  exclusions
       listed with smtp_tls_exclude_ciphers (see there for syntax details).

       Starting  with Postfix 2.6, the mandatory cipher exclusions can be specified on a per-des-
       tination basis via the TLS policy "exclude" attribute. See smtp_tls_policy_maps for  notes
       and examples.

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_protocols (default: !SSLv2)
       List of SSL/TLS protocols that the Postfix SMTP client will use with mandatory TLS encryp-
       tion.  In main.cf the values are separated by whitespace, commas or colons. In the  policy
       table  "protocols" attribute (see smtp_tls_policy_maps) the only valid separator is colon.
       An empty value means allow all protocols. The valid protocol names, (see \fBfBSSL_get_ver-
       sion(3)), are "SSLv2", "SSLv3" and "TLSv1".

       Note:  As  of  OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and "TLSv1.2". If an
       older Postfix version is linked against OpenSSL 1.0.1 or later, these, or  any  other  new
       protocol versions, are unconditionally enabled.

       With  Postfix  >= 2.5 the parameter syntax is expanded to support protocol exclusions. One
       can now explicitly exclude SSLv2 by setting "smtp_tls_mandatory_protocols  =  !SSLv2".  To
       exclude	both SSLv2 and SSLv3 set "smtp_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing
       the protocols to include, rather than protocols to exclude, is supported, but  not  recom-
       mended.	The  exclusion form more closely matches the behavior when the OpenSSL library is
       newer than Postfix.

       Since SSL version 2 has known protocol weaknesses and is now deprecated, the default  set-
       ting  excludes "SSLv2".	This means that by default, SSL version 2 will not be used at the
       "encrypt" security level and higher.

       See the documentation of the smtp_tls_policy_maps parameter and TLS_README for more infor-
       mation about security levels.

       Example:

       # Preferred form with Postfix >= 2.5:
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       # Alternative form.
       smtp_tls_mandatory_protocols = TLSv1

       This feature is available in Postfix 2.3 and later.

smtp_tls_note_starttls_offer (default: no)
       Log  the  hostname  of  a remote SMTP server that offers STARTTLS, when TLS is not already
       enabled for that server.

       The logfile record looks like:

       postfix/smtp[pid]:  Host offered STARTTLS: [name.of.host]

       This feature is available in Postfix 2.2 and later.

smtp_tls_per_site (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS usage policy by next-hop  destina-
       tion  and  by  remote  SMTP server hostname.  When both lookups succeed, the more specific
       per-site policy (NONE, MUST, etc) overrides the less specific  one  (MAY),  and	the  more
       secure per-site policy (MUST, etc) overrides the less secure one (NONE).  With Postfix 2.3
       and later smtp_tls_per_site is strongly discouraged: use smtp_tls_policy_maps instead.

       Use of the bare hostname as the per-site table lookup key is discouraged. Always  use  the
       full  destination  nexthop  (enclosed  in  [] with a possible ":port" suffix). A recipient
       domain or MX-enabled transport next-hop with no port suffix may look like a bare hostname,
       but is still a suitable destination.

       Specify	a next-hop destination or server hostname on the left-hand side; no wildcards are
       allowed. The next-hop destination is either the recipient domain, or the destination spec-
       ified  with  a transport(5) table, the relayhost parameter, or the relay_transport parame-
       ter.  On the right hand side specify one of the following keywords:

       NONE   Don't use TLS at all. This overrides a less specific MAY	lookup	result	from  the
	      alternate  host  or  next-hop  lookup  key,  and overrides the global smtp_use_tls,
	      smtp_enforce_tls, and smtp_tls_enforce_peername settings.

       MAY    Try to use TLS if the server announces support, otherwise use the unencrypted  con-
	      nection. This has less precedence than a more specific result (including NONE) from
	      the alternate host or next-hop lookup key, and has less precedence  than	the  more
	      specific global "smtp_enforce_tls = yes" or "smtp_tls_enforce_peername = yes".

       MUST_NOPEERMATCH
	      Require  TLS  encryption,  but  do not require that the remote SMTP server hostname
	      matches the information in the remote SMTP server certificate, or that  the  server
	      certificate was issued by a trusted CA. This overrides a less secure NONE or a less
	      specific MAY lookup result from the alternate host  or  next-hop	lookup	key,  and
	      overrides  the  global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peername
	      settings.

       MUST   Require TLS encryption, require that the remote SMTP server  hostname  matches  the
	      information in the remote SMTP server certificate, and require that the remote SMTP
	      server certificate was issued by a trusted CA. This overrides a  less  secure  NONE
	      and  MUST_NOPEERMATCH  or a less specific MAY lookup result from the alternate host
	      or next-hop lookup key, and overrides the global smtp_use_tls, smtp_enforce_tls and
	      smtp_tls_enforce_peername settings.

       The above keywords correspond to the "none", "may", "encrypt" and "verify" security levels
       for the new smtp_tls_security_level parameter introduced in  Postfix  2.3.  Starting  with
       Postfix	2.3,  and  independently  of  how  the	policy	is specified, the smtp_tls_manda-
       tory_ciphers and smtp_tls_mandatory_protocols parameters  apply	when  TLS  encryption  is
       mandatory.  Connections	for  which  encryption	is optional typically enable all "export"
       grade and better ciphers (see smtp_tls_ciphers and smtp_tls_protocols).

       As long as no secure DNS lookup mechanism is available, false hostnames	in  MX	or  CNAME
       responses  can  change  the  server  hostname  that Postfix uses for TLS policy lookup and
       server certificate verification. Even with a perfect match between the server hostname and
       the  server  certificate,  there  is  no  guarantee that Postfix is connected to the right
       server.	See TLS_README (Closing a DNS loophole with obsolete per-site TLS policies) for a
       possible work-around.

       This  feature  is  available  in  Postfix  2.2  and  later. With Postfix 2.3 and later use
       smtp_tls_policy_maps instead.

smtp_tls_policy_maps (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS security policy by next-hop desti-
       nation; when a non-empty value is specified, this overrides the obsolete smtp_tls_per_site
       parameter.  See TLS_README for a more detailed discussion of TLS security levels.

       The TLS policy table is indexed by the full next-hop  destination,  which  is  either  the
       recipient domain, or the verbatim next-hop specified in the transport table, $local_trans-
       port,  $virtual_transport,  $relay_transport  or  $default_transport.  This  includes  any
       enclosing  square  brackets  and  any non-default destination server port suffix. The LMTP
       socket type prefix (inet: or unix:) is not included in the lookup key.

       Only the next-hop domain, or $myhostname with LMTP over UNIX-domain sockets,  is  used  as
       the  nexthop name for certificate verification. The port and any enclosing square brackets
       are used in the table lookup key, but are not used for server name verification.

       When the lookup key is a domain name without enclosing square brackets or any :port suffix
       (typically  the	recipient domain), and the full domain is not found in the table, just as
       with the transport(5) table, the parent domain starting with  a	leading  "."  is  matched
       recursively.  This  allows one to specify a security policy for a recipient domain and all
       its sub-domains.

       The lookup result is a security level, followed by an optional list of  whitespace  and/or
       comma  separated  name=value  attributes  that  override related main.cf settings. The TLS
       security levels in order of increasing security are:

       none   No TLS. No additional attributes are supported at this level.

       may    Opportunistic TLS. Since sending in the clear  is  acceptable,  demanding  stronger
	      than default TLS security merely reduces inter-operability. The optional "ciphers",
	      "exclude" and "protocols" attributes (available for opportunistic TLS with  Postfix
	      >=   2.6)   override   the   "smtp_tls_ciphers",	 "smtp_tls_exclude_ciphers"   and
	      "smtp_tls_protocols" configuration parameters. When  opportunistic  TLS  handshakes
	      fail,  Postfix retries the connection with TLS disabled.	This allows mail delivery
	      to sites with non-interoperable TLS implementations.

       encrypt
	      Mandatory TLS encryption. At  this  level  and  higher,  the  optional  "protocols"
	      attribute   overrides   the  main.cf  smtp_tls_mandatory_protocols  parameter,  the
	      optional	"ciphers"  attribute  overrides  the  main.cf  smtp_tls_mandatory_ciphers
	      parameter,  and  the  optional  "exclude"  attribute (Postfix >= 2.6) overrides the
	      main.cf smtp_tls_mandatory_exclude_ciphers parameter. In the policy table, multiple
	      protocols  or excluded ciphers must be separated by colons, as attribute values may
	      not contain whitespace or commas.

       fingerprint
	      Certificate fingerprint verification. Available with Postfix 2.5 and later. At this
	      security level, there are no trusted certificate authorities. The certificate trust
	      chain, expiration date, ... are not checked. Instead, the optional match attribute,
	      or  else	the main.cf smtp_tls_fingerprint_cert_match parameter, lists the certifi-
	      cate fingerprints or the public key fingerprint (Postfix	2.9  and  later)  of  the
	      valid server certificate. The digest algorithm used to calculate the fingerprint is
	      selected by the smtp_tls_fingerprint_digest parameter. Multiple fingerprints can be
	      combined	with  a  "|"  delimiter  in  a	single match attribute, or multiple match
	      attributes can be employed. The ":" character is not used  as  a	delimiter  as  it
	      occurs between each pair of fingerprint (hexadecimal) digits.

       verify Mandatory  TLS verification.  At this security level, DNS MX lookups are trusted to
	      be secure enough, and the name  verified	in  the  server  certificate  is  usually
	      obtained	indirectly  via  unauthenticated  DNS  MX  lookups.  The optional "match"
	      attribute overrides the main.cf smtp_tls_verify_cert_match parameter. In the policy
	      table,  multiple	match  patterns  and  strategies must be separated by colons.  In
	      practice explicit control over matching is more common with  the	"secure"  policy,
	      described below.

       secure Secure-channel TLS. At this security level, DNS MX lookups, though potentially used
	      to determine the candidate next-hop gateway IP addresses, are  not  trusted  to  be
	      secure  enough for TLS peername verification. Instead, the default name verified in
	      the server certificate is obtained directly from the  next-hop,  or  is  explicitly
	      specified   via	the   optional	 match	attribute  which  overrides  the  main.cf
	      smtp_tls_secure_cert_match parameter. In the policy table, multiple match  patterns
	      and  strategies  must  be  separated by colons.  The match attribute is most useful
	      when multiple domains are supported by common server, the policy entries for  addi-
	      tional  domains  specify	matching  rules for the primary domain certificate. While
	      transport table overrides routing the secondary domains to the primary nexthop also
	      allow secure verification, they risk delivery to the wrong destination when domains
	      change hands or are  re-assigned	to  new  gateways.  With  the  "match"	attribute
	      approach,  routing  is not perturbed, and mail is deferred if verification of a new
	      MX host fails.

       Example:

       /etc/postfix/main.cf:
	   smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
	   # Postfix 2.5 and later
	   smtp_tls_fingerprint_digest = md5

       /etc/postfix/tls_policy:
	   example.edu		       none
	   example.mil		       may
	   example.gov		       encrypt protocols=TLSv1
	   example.com		       verify ciphers=high
	   example.net		       secure
	   .example.net 	       secure match=.example.net:example.net
	   [mail.example.org]:587      secure match=nexthop
	   # Postfix 2.5 and later
	   [thumb.example.org]		fingerprint
	    match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
	    match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1

       Note:   The   hostname	strategy   if	listed	  in	a    non-default    setting    of
       smtp_tls_secure_cert_match  or  in  the match attribute in the policy table can render the
       secure level vulnerable to DNS forgery. Do not use the hostname strategy for  secure-chan-
       nel configurations in environments where DNS security is not assured.

       This feature is available in Postfix 2.3 and later.

smtp_tls_protocols (default: !SSLv2)
       List  of  TLS  protocols  that the Postfix SMTP client will exclude or include with oppor-
       tunistic TLS encryption. Starting with Postfix  2.6,  the  Postfix  SMTP  client  will  by
       default not use the obsolete SSLv2 protocol.

       In  main.cf  the values are separated by whitespace, commas or colons. In the policy table
       (see smtp_tls_policy_maps) the only valid separator is colon. An empty value  means  allow
       all  protocols.	The  valid  protocol  names,  (see \fBfBSSL_get_version(3)), are "SSLv2",
       "SSLv3" and "TLSv1".

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and  "TLSv1.2".  If  an
       older  Postfix  version	is linked against OpenSSL 1.0.1 or later, these, or any other new
       protocol versions, are unconditionally enabled.

       To include a protocol list its name, to exclude it, prefix the name with a "!"  character.
       To  exclude SSLv2 even for opportunistic TLS set "smtp_tls_protocols = !SSLv2". To exclude
       both "SSLv2" and "SSLv3" set "smtp_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the
       protocols to include, rather than protocols to exclude, is supported, but not recommended.
       The exclusion form more closely matches the behavior when the  OpenSSL  library	is  newer
       than Postfix.

       Example:
       # TLSv1 only!
       smtp_tls_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.6 and later.

smtp_tls_scert_verifydepth (default: 9)
       The  verification depth for remote SMTP server certificates. A depth of 1 is sufficient if
       the issuing CA is listed in a local CA file.

       The default verification depth is 9 (the OpenSSL default) for compatibility  with  earlier
       Postfix	behavior.  Prior  to  Postfix 2.5, the default value was 5, but the limit was not
       actually enforced. If you have set this to a lower non-default  value,  certificates  with
       longer trust chains may now fail to verify. Certificate chains with 1 or 2 CAs are common,
       deeper chains are more rare and any number between 5 and 9 should suffice in practice. You
       can  choose  a  lower number if, for example, you trust certificates directly signed by an
       issuing CA but not any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtp_tls_secure_cert_match (default: nexthop, dot-nexthop)
       How the Postfix SMTP client verifies the server certificate peername for the "secure"  TLS
       security  level. In a "secure" TLS policy table ($smtp_tls_policy_maps) entry the optional
       "match" attribute overrides this main.cf setting.

       This parameter specifies one or more patterns or strategies separated  by  commas,  white-
       space or colons.  In the policy table the only valid separator is the colon character.

       For  a  description  of the pattern and strategy syntax see the smtp_tls_verify_cert_match
       parameter. The "hostname" strategy should be avoided in this context, as in the absence of
       a  secure  global  DNS, using the results of MX lookups in certificate verification is not
       immune to active (man-in-the-middle) attacks on DNS.

       Sample main.cf setting:

	   smtp_tls_secure_cert_match = nexthop

       Sample policy table override:

	   example.net	   secure match=example.com:.example.com
	   .example.net    secure match=example.com:.example.com

       This feature is available in Postfix 2.3 and later.

smtp_tls_security_level (default: empty)
       The default SMTP TLS security level for the Postfix SMTP client; when a non-empty value is
       specified,  this  overrides  the  obsolete  parameters smtp_use_tls, smtp_enforce_tls, and
       smtp_tls_enforce_peername.

       Specify one of the following security levels:

       none   TLS will not be used unless enabled for  specific  destinations  via  smtp_tls_pol-
	      icy_maps.

       may    Opportunistic  TLS.  Use TLS if this is supported by the remote SMTP server, other-
	      wise use plaintext. Since sending in the clear is  acceptable,  demanding  stronger
	      than default TLS security merely reduces inter-operability.  The "smtp_tls_ciphers"
	      and "smtp_tls_protocols" (Postfix >= 2.6) configuration parameters provide  control
	      over  the  protocols  and  cipher  grade used with opportunistic TLS.  With earlier
	      releases the opportunistic TLS cipher grade is always "export" and no protocols are
	      disabled.   When	TLS handshakes fail, the connection is retried with TLS disabled.
	      This allows mail delivery to sites with non-interoperable TLS implementations.

       encrypt
	      Mandatory TLS encryption. Since a minimum level of security is intended, it is rea-
	      sonable  to be specific about sufficiently secure protocol versions and ciphers. At
	      this security level and higher, the main.cf parameters smtp_tls_mandatory_protocols
	      and  smtp_tls_mandatory_ciphers  specify the TLS protocols and minimum cipher grade
	      which the administrator considers secure enough for mandatory  encrypted	sessions.
	      This  security  level  is not an appropriate default for systems delivering mail to
	      the Internet.

       fingerprint
	      Certificate fingerprint verification. Available with Postfix 2.5 and later. At this
	      security level, there are no trusted certificate authorities. The certificate trust
	      chain,  expiration  date,  ...  are  not	checked.  Instead,  the  smtp_tls_finger-
	      print_cert_match	parameter lists the certificate fingerprint or public key finger-
	      print (Postfix 2.9 and later) of the valid server certificate. The digest algorithm
	      used  to	calculate  the fingerprint is selected by the smtp_tls_fingerprint_digest
	      parameter.

       verify Mandatory TLS verification. At this security level, DNS MX lookups are  trusted  to
	      be  secure  enough,  and	the  name  verified  in the server certificate is usually
	      obtained	indirectly  via  unauthenticated  DNS  MX  lookups.   The   smtp_tls_ver-
	      ify_cert_match  parameter  controls  how	the  server name is verified. In practice
	      explicit control over matching is more common  at  the  "secure"	level,	described
	      below.  This  security  level  is not an appropriate default for systems delivering
	      mail to the Internet.

       secure Secure-channel TLS.  At this security level, DNS	MX  lookups,  though  potentially
	      used  to	determine the candidate next-hop gateway IP addresses, are not trusted to
	      be secure enough for TLS peername verification. Instead, the default name  verified
	      in  the server certificate is obtained from the next-hop domain as specified in the
	      smtp_tls_secure_cert_match configuration parameter. The default  matching  rule  is
	      that  a  server certificate matches when its name is equal to or is a sub-domain of
	      the nexthop domain. This security level is not an appropriate default  for  systems
	      delivering mail to the Internet.

       Examples:

       # No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
       smtp_tls_security_level = none

       # Opportunistic TLS.
       smtp_tls_security_level = may
       # Postfix >= 2.6:
       # Do not tweak opportunistic ciphers or protocol unless it is essential
       # to do so (if a security vulnerability is found in the SSL library that
       # can be mitigated by disabling a particular protocol or raising the
       # cipher grade from "export" to "low" or "medium").
       smtp_tls_ciphers = export
       smtp_tls_protocols = !SSLv2

       # Mandatory (high-grade) TLS encryption.
       smtp_tls_security_level = encrypt
       smtp_tls_mandatory_ciphers = high

       # Mandatory TLS verification of hostname or nexthop domain.
       smtp_tls_security_level = verify
       smtp_tls_mandatory_ciphers = high
       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       # Secure channel TLS with exact nexthop name match.
       smtp_tls_security_level = secure
       smtp_tls_mandatory_protocols = TLSv1
       smtp_tls_mandatory_ciphers = high
       smtp_tls_secure_cert_match = nexthop

       # Certificate fingerprint verification (Postfix >= 2.5).
       # The CA-less "fingerprint" security level only scales to a limited
       # number of destinations. As a global default rather than a per-site
       # setting, this is practical when mail for all recipients is sent
       # to a central mail hub.
       relayhost = [mailhub.example.com]
       smtp_tls_security_level = fingerprint
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       smtp_tls_mandatory_ciphers = high
       smtp_tls_fingerprint_cert_match =
	   3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
	   EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.3 and later.

smtp_tls_session_cache_database (default: empty)
       Name  of the file containing the optional Postfix SMTP client TLS session cache. Specify a
       database type that supports enumeration, such as btree or sdbm; there is no need  to  sup-
       port concurrent access.	The file is created if it does not exist. The smtp(8) daemon does
       not use this parameter directly,  rather  the  cache  is  implemented  indirectly  in  the
       tlsmgr(8)  daemon. This means that per-smtp-instance master.cf overrides of this parameter
       are not effective.  Note, that each of the cache databases supported by tlsmgr(8)  daemon:
       $smtpd_tls_session_cache_database,  $smtp_tls_session_cache_database (and with Postfix 2.3
       and later $lmtp_tls_session_cache_database), needs to be stored separately. It is  not  at
       this time possible to store multiple caches in a single database.

       Note: dbm databases are not suitable. TLS session objects are too large.

       As of version 2.5, Postfix no longer uses root privileges when opening this file. The file
       should now be stored under the  Postfix-owned  data_directory.  As  a  migration  aid,  an
       attempt	to open the file under a non-Postfix directory is redirected to the Postfix-owned
       data_directory, and a warning is logged.

       Example:

       smtp_tls_session_cache_database = btree:/var/lib/postfix/smtp_scache

       This feature is available in Postfix 2.2 and later.

smtp_tls_session_cache_timeout (default: 3600s)
       The expiration time of Postfix SMTP client TLS session cache information.  A cache cleanup
       is   performed	periodically   every  $smtp_tls_session_cache_timeout  seconds.  As  with
       $smtp_tls_session_cache_database, this parameter is implemented in  the	tlsmgr(8)  daemon
       and therefore per-smtp-instance master.cf overrides are not possible.

       This feature is available in Postfix 2.2 and later.

smtp_tls_verify_cert_match (default: hostname)
       How  the Postfix SMTP client verifies the server certificate peername for the "verify" TLS
       security level. In a "verify" TLS policy table ($smtp_tls_policy_maps) entry the  optional
       "match" attribute overrides this main.cf setting.

       This  parameter	specifies  one or more patterns or strategies separated by commas, white-
       space or colons.  In the policy table the only valid separator is the colon character.

       Patterns specify domain names, or domain name suffixes:

       example.com
	      Match the example.com domain, i.e. one of the names the server certificate must  be
	      example.com, upper and lower case distinctions are ignored.

       .example.com
	      Match  subdomains  of  the example.com domain, i.e. match a name in the server cer-
	      tificate that consists of a non-zero number of labels followed  by  a  .example.com
	      suffix. Case distinctions are ignored.

       Strategies  specify  a transformation from the next-hop domain to the expected name in the
       server certificate:

       nexthop
	      Match against the next-hop domain, which is either the  recipient  domain,  or  the
	      transport  next-hop  configured for the domain stripped of any optional socket type
	      prefix, enclosing square brackets and trailing port. When MX lookups are	not  sup-
	      pressed, this is the original nexthop domain prior to the MX lookup, not the result
	      of the MX lookup. For LMTP delivery via UNIX-domain sockets, the verified  next-hop
	      name  is	$myhostname.  This strategy is suitable for use with the "secure" policy.
	      Case is ignored.

       dot-nexthop
	      As above, but match server certificate names that are subdomains	of  the  next-hop
	      domain. Case is ignored.

       hostname
	      Match against the hostname of the server, often obtained via an unauthenticated DNS
	      MX lookup. For LMTP delivery via UNIX-domain sockets, the verified name is $myhost-
	      name.  This matches the verification strategy of the "MUST" keyword in the obsolete
	      smtp_tls_per_site table, and is suitable for use with the "verify" security  level.
	      When  the  next-hop name is enclosed in square brackets to suppress MX lookups, the
	      "hostname" strategy is the same as the "nexthop" strategy. Case is ignored.

       Sample main.cf setting:

       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       Sample policy table override:

       example.com     verify  match=hostname:nexthop
       .example.com    verify  match=example.com:.example.com:hostname

       This feature is available in Postfix 2.3 and later.

smtp_use_tls (default: no)
       Opportunistic mode: use TLS when a remote SMTP server announces STARTTLS  support,  other-
       wise  send  the	mail in the clear. Beware: some SMTP servers offer STARTTLS even if it is
       not configured.	With Postfix < 2.3, if the TLS handshake fails, and no	other  server  is
       available, delivery is deferred and mail stays in the queue. If this is a concern for you,
       use the smtp_tls_per_site feature instead.

       This feature is available in Postfix 2.2  and  later.  With  Postfix  2.3  and  later  use
       smtp_tls_security_level instead.

smtp_xforward_timeout (default: 300s)
       The Postfix SMTP client time limit for sending the XFORWARD command, and for receiving the
       remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_authorized_verp_clients (default: $authorized_verp_clients)
       What  remote SMTP clients are allowed to specify the XVERP command.  This command requests
       that mail be delivered one recipient at a time with a per recipient return address.

       By default, no clients are allowed to specify XVERP.

       This parameter was renamed with Postfix version 2.1. The default value is  backwards  com-
       patible with Postfix version 2.0.

       Specify	a  list  of  network/netmask patterns, separated by commas and/or whitespace. The
       mask specifies the number of bits in the network part of a  host  address.  You	can  also
       specify	hostnames  or  .domain names (the initial dot causes the domain to match any name
       below it),  "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced  by
       its  contents;  a "type:table" lookup table is matched when a table entry matches a lookup
       string (the lookup result is ignored).  Continue long lines by starting the next line with
       whitespace.  Specify  "!pattern" to exclude an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside	[]  in	the  smtpd_autho-
       rized_verp_clients  value,  and	in  files  specified  with  "/file/name".   IP	version 6
       addresses contain the ":" character, and would otherwise be confused with  a  "type:table"
       pattern.

smtpd_authorized_xclient_hosts (default: empty)
       What  remote  SMTP clients are allowed to use the XCLIENT feature.  This command overrides
       remote SMTP client information that is used for access control. Typical use is  for  SMTP-
       based  content  filters,  fetchmail-like programs, or SMTP server access rule testing. See
       the XCLIENT_README document for details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XCLIENT.

       Specify a list of network/netmask patterns, separated by  commas  and/or  whitespace.  The
       mask  specifies	the  number  of  bits in the network part of a host address. You can also
       specify hostnames or .domain names (the initial dot causes the domain to  match	any  name
       below  it),  "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced by
       its contents; a "type:table" lookup table is matched when a table entry matches	a  lookup
       string (the lookup result is ignored).  Continue long lines by starting the next line with
       whitespace. Specify "!pattern" to exclude an address or network block from the  list.  The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:  IP  version  6  address information must be specified inside [] in the smtpd_autho-
       rized_xclient_hosts value, and  in  files  specified  with  "/file/name".   IP  version	6
       addresses  contain  the ":" character, and would otherwise be confused with a "type:table"
       pattern.

smtpd_authorized_xforward_hosts (default: empty)
       What remote SMTP clients are allowed to use the XFORWARD feature.  This	command  forwards
       information  that  is  used  to	improve logging after SMTP-based content filters. See the
       XFORWARD_README document for details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XFORWARD.

       Specify a list of network/netmask patterns, separated by  commas  and/or  whitespace.  The
       mask  specifies	the  number  of  bits in the network part of a host address. You can also
       specify hostnames or .domain names (the initial dot causes the domain to  match	any  name
       below  it),  "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced by
       its contents; a "type:table" lookup table is matched when a table entry matches	a  lookup
       string (the lookup result is ignored).  Continue long lines by starting the next line with
       whitespace. Specify "!pattern" to exclude an address or network block from the  list.  The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:  IP  version  6  address information must be specified inside [] in the smtpd_autho-
       rized_xforward_hosts value, and in  files  specified  with  "/file/name".   IP  version	6
       addresses  contain  the ":" character, and would otherwise be confused with a "type:table"
       pattern.

smtpd_banner (default: $myhostname ESMTP $mail_name)
       The text that follows the 220 status code in the SMTP greeting banner. Some people like to
       see the mail version advertised. By default, Postfix shows no version.

       You MUST specify $myhostname at the start of the text. This is required by the SMTP proto-
       col.

       Example:

       smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

smtpd_client_connection_count_limit (default: 50)
       How many simultaneous connections any client is allowed	to  make  to  this  service.   By
       default, the limit is set to half the default process limit value.

       To disable this feature, specify a limit of 0.

       WARNING:  The  purpose  of this feature is to limit abuse. It must not be used to regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

smtpd_client_connection_rate_limit (default: 0)
       The maximal number of connection attempts any client is allowed to make	to  this  service
       per  time  unit.   The  time unit is specified with the anvil_rate_time_unit configuration
       parameter.

       By default, a client can make as many connections per time unit as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not be  used  to  regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_connection_rate_limit = 1000

smtpd_client_event_limit_exceptions (default: $mynetworks)
       Clients	that  are  excluded  from  smtpd_client_*_count/rate_limit  restrictions. See the
       mynetworks parameter description for the parameter value syntax.

       By default, clients in trusted networks are excluded. Specify a list  of  network  blocks,
       hostnames or .domain names (the initial dot causes the domain to match any name below it).

       Note:   IP   version   6   address   information  must  be  specified  inside  []  in  the
       smtpd_client_event_limit_exceptions value, and in files specified with  "/file/name".   IP
       version	6  addresses  contain  the  ":" character, and would otherwise be confused with a
       "type:table" pattern.

       This feature is available in Postfix 2.2 and later.

smtpd_client_message_rate_limit (default: 0)
       The maximal number of message delivery requests that any client is allowed to make to this
       service	per  time  unit, regardless of whether or not Postfix actually accepts those mes-
       sages.  The time unit is specified with the anvil_rate_time_unit configuration parameter.

       By default, a client can send as many message delivery requests per time unit  as  Postfix
       can accept.

       To disable this feature, specify a limit of 0.

       WARNING:  The  purpose  of this feature is to limit abuse. It must not be used to regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_message_rate_limit = 1000

smtpd_client_new_tls_session_rate_limit (default: 0)
       The maximal number of new (i.e., uncached) TLS sessions	that  a  remote  SMTP  client  is
       allowed to negotiate with this service per time unit.  The time unit is specified with the
       anvil_rate_time_unit configuration parameter.

       By default, a remote SMTP client can negotiate as many new TLS sessions per time  unit  as
       Postfix can accept.

       To disable this feature, specify a limit of 0. Otherwise, specify a limit that is at least
       the per-client concurrent session  limit,  or  else  legitimate	client	sessions  may  be
       rejected.

       WARNING:  The  purpose  of this feature is to limit abuse. It must not be used to regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.3 and later.

       Example:

       smtpd_client_new_tls_session_rate_limit = 100

smtpd_client_port_logging (default: no)
       Enable logging of the remote SMTP client port in addition to the hostname and IP  address.
       The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

smtpd_client_recipient_rate_limit (default: 0)
       The  maximal number of recipient addresses that any client is allowed to send to this ser-
       vice per time unit, regardless of whether or not Postfix actually  accepts  those  recipi-
       ents.  The time unit is specified with the anvil_rate_time_unit configuration parameter.

       By  default,  a	client	can send as many recipient addresses per time unit as Postfix can
       accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not be  used  to  regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_recipient_rate_limit = 1000

smtpd_client_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the context of a client con-
       nection request.  See SMTPD_ACCESS_README, section  "Delayed  evaluation  of  SMTP  access
       restriction lists" for a discussion of evaluation context and time.

       The default is to allow all connection requests.

       Specify	a  list  of  restrictions,  separated by commas and/or whitespace.  Continue long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The  following  restrictions  are  specific  to	client hostname or client network address
       information.

       check_ccert_access type:table
	      Use the remote SMTP client certificate fingerprint or the  public  key  fingerprint
	      (Postfix	2.9  and  later) as lookup key for the specified access(5) database; with
	      Postfix version 2.2, also require that the remote SMTP client certificate is  veri-
	      fied  successfully.   The  fingerprint  digest  algorithm  is  configurable via the
	      smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to Postfix  version
	      2.5).  This feature is available with Postfix version 2.2 and later.

       check_client_access type:table
	      Search  the  specified  access  database	for  the client hostname, parent domains,
	      client IP address, or networks obtained by stripping least significant octets.  See
	      the access(5) manual page for details.

       check_client_mx_access type:table
	      Search  the  specified access(5) database for the MX hosts for the client hostname,
	      and execute the corresponding action.  Note: a result of "OK" is	not  allowed  for
	      safety  reasons.	Instead, use DUNNO in order to exclude specific hosts from black-
	      lists.  This feature is available in Postfix 2.7 and later.

       check_client_ns_access type:table
	      Search the specified access(5) database for the DNS servers for  the  client  host-
	      name,  and execute the corresponding action.  Note: a result of "OK" is not allowed
	      for safety reasons. Instead, use DUNNO in order  to  exclude  specific  hosts  from
	      blacklists.  This feature is available in Postfix 2.7 and later.

       check_reverse_client_hostname_access type:table
	      Search  the  specified  access database for the unverified reverse client hostname,
	      parent domains, client IP address, or networks obtained by stripping least signifi-
	      cant  octets. See the access(5) manual page for details.	Note: a result of "OK" is
	      not allowed for safety reasons.  Instead, use DUNNO in order  to	exclude  specific
	      hosts from blacklists.  This feature is available in Postfix 2.6 and later.

       check_reverse_client_hostname_mx_access type:table
	      Search the specified access(5) database for the MX hosts for the unverified reverse
	      client hostname, and execute the corresponding action.  Note: a result of  "OK"  is
	      not  allowed  for  safety reasons.  Instead, use DUNNO in order to exclude specific
	      hosts from blacklists.  This feature is available in Postfix 2.7 and later.

       check_reverse_client_hostname_ns_access type:table
	      Search the specified access(5) database for the  DNS  servers  for  the  unverified
	      reverse  client  hostname, and execute the corresponding action.	Note: a result of
	      "OK" is not allowed for safety reasons.  Instead, use DUNNO  in  order  to  exclude
	      specific	hosts  from  blacklists.   This  feature  is available in Postfix 2.7 and
	      later.

       permit_inet_interfaces
	      Permit the request when the client IP address matches $inet_interfaces.

       permit_mynetworks
	      Permit the request when the client  IP  address  matches	any  network  or  network
	      address listed in  $mynetworks.

       permit_sasl_authenticated
	      Permit  the  request when the client is successfully authenticated via the RFC 4954
	      (AUTH) protocol.

       permit_tls_all_clientcerts
	      Permit the request when the remote SMTP client  certificate  is  verified  success-
	      fully.   This  option must be used only if a special CA issues the certificates and
	      only this CA is listed as trusted CA. Otherwise, clients with  a	third-party  cer-
	      tificate would also be allowed to relay.	Specify "tls_append_default_CA = no" when
	      the trusted CA is specified with smtpd_tls_CAfile or smtpd_tls_CApath,  to  prevent
	      Postfix  from appending the system-supplied default CAs.	This feature is available
	      with Postfix version 2.2.

       permit_tls_clientcerts
	      Permit the request when the remote SMTP client certificate  fingerprint  or  public
	      key  fingerprint (Postfix 2.9 and later) is listed in $relay_clientcerts.  The fin-
	      gerprint digest algorithm  is  configurable  via	the  smtpd_tls_fingerprint_digest
	      parameter (hard-coded as md5 prior to Postfix version 2.5).  This feature is avail-
	      able with Postfix version 2.2.

       reject_rbl_client rbl_domain=d.d.d.d
	      Reject the request when the reversed client network address is listed  with  the	A
	      record  "d.d.d.d"  under rbl_domain (Postfix version 2.1 and later only).  Each "d"
	      is a number, or a pattern inside "[]" that contains one or more ";"-separated  num-
	      bers or number..number ranges (Postfix version 2.8 and later).  If no "=d.d.d.d" is
	      specified, reject the request when the reversed client network  address  is  listed
	      with any A record under rbl_domain.
	      The  maps_rbl_reject_code  parameter  specifies  the  response  code  for  rejected
	      requests (default:  554), the default_rbl_reply  parameter  specifies  the  default
	      server  reply,  and  the	rbl_reply_maps	 parameter  specifies  tables with server
	      replies indexed by rbl_domain.  This feature is available in Postfix 2.0 and later.

       permit_dnswl_client dnswl_domain=d.d.d.d
	      Accept the request when the reversed client network address is listed  with  the	A
	      record  "d.d.d.d"  under	dnswl_domain.	Each "d" is a number, or a pattern inside
	      "[]" that contains one or more ";"-separated numbers or number..number ranges.   If
	      no  "=d.d.d.d"  is  specified,  accept the request when the reversed client network
	      address is listed with any A record under dnswl_domain.
	      For  safety,  permit_dnswl_client  is  silently  ignored	when  it  would  override
	      reject_unauth_destination.   The	result	is  DEFER_IF_REJECT when whitelist lookup
	      fails.  This feature is available in Postfix 2.8 and later.

       reject_rhsbl_client rbl_domain=d.d.d.d
	      Reject the request when the client hostname is listed with the A	record	"d.d.d.d"
	      under  rbl_domain (Postfix version 2.1 and later only).  Each "d" is a number, or a
	      pattern inside "[]" that contains one or more ";"-separated numbers or number..num-
	      ber  ranges (Postfix version 2.8 and later).  If no "=d.d.d.d" is specified, reject
	      the request when the client hostname is listed with any A record under  rbl_domain.
	      See  the	reject_rbl_client description above for additional RBL related configura-
	      tion parameters.	This feature is available in Postfix 2.0 and later; with  Postfix
	      version  2.8  and  later,  reject_rhsbl_reverse_client  will usually produce better
	      results.

       permit_rhswl_client rhswl_domain=d.d.d.d
	      Accept the request when the client hostname is listed with the A	record	"d.d.d.d"
	      under  rhswl_domain.   Each "d" is a number, or a pattern inside "[]" that contains
	      one or more ";"-separated numbers or number..number ranges.  If  no  "=d.d.d.d"  is
	      specified,  accept the request when the client hostname is listed with any A record
	      under rhswl_domain.
	      Caution: client name whitelisting is fragile, since the client name lookup can fail
	      due  to  temporary outages.  Client name whitelisting should be used only to reduce
	      false positives in e.g.  DNS-based blocklists,  and  not	for  making  access  rule
	      exceptions.
	      For  safety,  permit_rhswl_client  is  silently  ignored	when  it  would  override
	      reject_unauth_destination.  The result is  DEFER_IF_REJECT  when	whitelist  lookup
	      fails.  This feature is available in Postfix 2.8 and later.

       reject_rhsbl_reverse_client rbl_domain=d.d.d.d
	      Reject the request when the unverified reverse client hostname is listed with the A
	      record "d.d.d.d" under rbl_domain.  Each "d" is a number, or a pattern inside  "[]"
	      that  contains  one  or more ";"-separated numbers or number..number ranges.  If no
	      "=d.d.d.d" is specified, reject the request  when  the  unverified  reverse  client
	      hostname	is  listed  with any A record under rbl_domain. See the reject_rbl_client
	      description above for additional RBL related configuration parameters.   This  fea-
	      ture is available in Postfix 2.8 and later.

       reject_unknown_client_hostname (with Postfix < 2.3: reject_unknown_client)
	      Reject  the  request  when  1)  the  client  IP address->name mapping fails, 2) the
	      name->address mapping fails, or 3) the name->address mapping  does  not  match  the
	      client IP address.
	      This is a stronger restriction than the reject_unknown_reverse_client_hostname fea-
	      ture, which triggers only under condition 1) above.
	      The unknown_client_reject_code parameter specifies the response code  for  rejected
	      requests	(default:  450).  The  reply  is  always 450 in case the address->name or
	      name->address lookup failed due to a temporary problem.

       reject_unknown_reverse_client_hostname
	      Reject the request when the client IP address has no address->name mapping.
	      This is a weaker restriction than the reject_unknown_client_hostname feature, which
	      requires not only that the address->name and name->address mappings exist, but also
	      that the two mappings reproduce the client IP address.
	      The unknown_client_reject_code parameter specifies the response code  for  rejected
	      requests	(default: 450).  The reply is always 450 in case the address->name lookup
	      failed due to a temporary problem.
	      This feature is available in Postfix 2.3 and later.

       In addition, you can use any of the following generic  restrictions.   These  restrictions
       are applicable in any SMTP command context.

       check_policy_service servername
	      Query  the  specified  policy  server.  See  the	SMTPD_POLICY_README  document for
	      details. This feature is available in Postfix 2.1 and later.

       defer  Defer the request. The client is told to try again later. This restriction is  use-
	      ful at the end of a restriction list, to make the default policy explicit.
	      The defer_code parameter specifies the SMTP server reply code (default: 450).

       defer_if_permit
	      Defer the request if some later restriction would result in an explicit or implicit
	      PERMIT action.  This is useful when a blacklisting feature fails due to a temporary
	      problem.	This feature is available in Postfix version 2.1 and later.

       defer_if_reject
	      Defer  the request if some later restriction would result in a REJECT action.  This
	      is useful when a whitelisting feature fails due to a temporary problem.  This  fea-
	      ture is available in Postfix version 2.1 and later.

       permit Permit the request. This restriction is useful at the end of a restriction list, to
	      make the default policy explicit.

       reject_multi_recipient_bounce
	      Reject the request when the envelope sender is the null address,	and  the  message
	      has  multiple envelope recipients. This usage has rare but legitimate applications:
	      under certain conditions, multi-recipient mail that was posted with the DSN  option
	      NOTIFY=NEVER may be forwarded with the null sender address.
	      Note:  this restriction can only work reliably when used in smtpd_data_restrictions
	      or smtpd_end_of_data_restrictions, because the total number of  recipients  is  not
	      known  at  an  earlier  stage of the SMTP conversation.  Use at the RCPT stage will
	      only reject the second etc.  recipient.
	      The multi_recipient_bounce_reject_code parameter specifies the  response	code  for
	      rejected	requests  (default:   550).  This feature is available in Postfix 2.1 and
	      later.

       reject_plaintext_session
	      Reject the request when the connection is not encrypted.	This  restriction  should
	      not  be  used  before  the client has had a chance to negotiate encryption with the
	      AUTH or STARTTLS commands.
	      The plaintext_reject_code  parameter  specifies  the  response  code  for  rejected
	      requests (default:  450).  This feature is available in Postfix 2.3 and later.

       reject_unauth_pipelining
	      Reject  the  request  when the client sends SMTP commands ahead of time where it is
	      not allowed, or when the client sends SMTP commands ahead of time  without  knowing
	      that  Postfix actually supports ESMTP command pipelining. This stops mail from bulk
	      mail software that improperly uses ESMTP command pipelining in order  to	speed  up
	      deliveries.
	      With  Postfix  2.6  and  later, the SMTP server sets a per-session flag whenever it
	      detects  illegal	pipelining,  including	pipelined  EHLO  or  HELO  commands.  The
	      reject_unauth_pipelining feature simply tests whether the flag was set at any point
	      in time during the session.
	      With older Postfix versions, reject_unauth_pipelining checks the current status  of
	      the  input  read	queue,	and  its  usage is not recommended in contexts other than
	      smtpd_data_restrictions.

       reject Reject the request. This restriction is useful at the end of a restriction list, to
	      make  the  default policy explicit.  The reject_code configuration parameter speci-
	      fies the response code for rejected requests (default: 554).

       sleep seconds
	      Pause for the specified number of seconds and proceed with the next restriction  in
	      the list, if any. This may stop zombie mail when used as:
	      /etc/postfix/main.cf:
		  smtpd_client_restrictions =
		      sleep 1, reject_unauth_pipelining
		  smtpd_delay_reject = no
	      This feature is available in Postfix 2.3.

       warn_if_reject
	      A  safety  net  for  testing.  When "warn_if_reject" is placed before a reject-type
	      restriction, access  table  query,  or  check_policy_service  query,  this  logs	a
	      "reject_warning"	message  instead  of  rejecting  a  request  (when  a reject-type
	      restriction fails due to a temporary error, this logs  a	"reject_warning"  message
	      for  any	implicit  "defer_if_permit" actions that would normally prevent mail from
	      being accepted by some later access restriction). This feature  has  no  effect  on
	      defer_if_reject restrictions.

       Other restrictions that are valid in this context:

       o      SMTP command specific restrictions that are described under the smtpd_helo_restric-
	      tions, smtpd_sender_restrictions or smtpd_recipient_restrictions	parameters.  When
	      helo,  sender or recipient restrictions are listed under smtpd_client_restrictions,
	      they   have   effect   only   with   "smtpd_delay_reject	 =    yes",    so    that
	      $smtpd_client_restrictions is evaluated at the time of the RCPT TO command.

       Example:

       smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname

smtpd_command_filter (default: empty)
       A mechanism to transform commands from remote SMTP clients.  This is a last-resort tool to
       work around client commands that break inter-operability with  the  Postfix  SMTP  server.
       Other uses involve fault injection to test Postfix's handling of invalid commands.

       Specify	the name of a "type:table" lookup table. The search string is the SMTP command as
       received from the remote SMTP client, except that  initial  whitespace  and  the  trailing
       <CR><LF> are removed.  The result value is executed by the Postfix SMTP server.

       There is no need to use smtpd_command_filter for the following cases:

       o      Use "resolve_numeric_domain = yes" to accept "user@ipaddress".

       o      Postfix already accepts the correct form "user@[ipaddress]". Use virtual_alias_maps
	      or canonical_maps to translate these into domain names if necessary.

       o      Use "strict_rfc821_envelopes =  no"  to  accept  "RCPT  TO:<User	Name  <user@exam-
	      ple.com>>". Postfix will ignore the "User Name" part and deliver to the <user@exam-
	      ple.com> address.

       Examples of problems that can be solved with the smtpd_command_filter feature:

       /etc/postfix/main.cf:
	   smtpd_command_filter = pcre:/etc/postfix/command_filter

       /etc/postfix/command_filter:
	   # Work around clients that send malformed HELO commands.
	   /^HELO\s*$/ HELO domain.invalid

	   # Work around clients that send empty lines.
	   /^\s*$/     NOOP

	   # Work around clients that send RCPT TO:<'user@domain'>.
	   # WARNING: do not lose the parameters that follow the address.
	   /^RCPT\s+TO:\s*<'([^[:space:]]+)'>(.*)/     RCPT TO:<$1>$2

	   # Append XVERP to MAIL FROM commands to request VERP-style delivery.
	   # See VERP_README for more information on how to use Postfix VERP.
	   /^(MAIL FROM:<listname@example\.com>.*)/   $1 XVERP

	   # Bounce-never mail sink. Use notify_classes=bounce,resource,software
	   # to send bounced mail to the postmaster (with message body removed).
	   /^(RCPT\s+TO:<.*>.*)\s+NOTIFY=\S+(.*)/ $1 NOTIFY=NEVER$2
	   /^(RCPT\s+TO:.*)/			$1 NOTIFY=NEVER

       This feature is available in Postfix 2.7.

smtpd_data_restrictions (default: empty)
       Optional access restrictions that the Postfix SMTP server applies in the  context  of  the
       SMTP  DATA  command.   See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
       restriction lists" for a discussion of evaluation context and time.

       This feature is available in Postfix 2.0 and later.

       Specify a list of restrictions, separated by  commas  and/or  whitespace.   Continue  long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The following restrictions are valid in this context:

       o      Generic restrictions that can be used in any SMTP command context, described  under
	      smtpd_client_restrictions.

       o      SMTP  command  specific  restrictions  described	under  smtpd_client_restrictions,
	      smtpd_helo_restrictions, smtpd_sender_restrictions or smtpd_recipient_restrictions.

       o      However, no recipient information is available in the case of multi-recipient mail.
	      Acting  on only one recipient would be misleading, because any decision will affect
	      all recipients equally. Acting on all recipients	would  require	a  possibly  very
	      large  amount  of  memory,  and  would also be misleading for the reasons mentioned
	      before.

       Examples:

       smtpd_data_restrictions = reject_unauth_pipelining
       smtpd_data_restrictions = reject_multi_recipient_bounce

smtpd_delay_open_until_valid_rcpt (default: yes)
       Postpone the start of an SMTP mail transaction until a valid RCPT TO command is	received.
       Specify	"no"  to  create a mail transaction as soon as the Postfix SMTP server receives a
       valid MAIL FROM command.

       With sites that reject lots of mail, the default setting reduces the use of disk, CPU  and
       memory resources. The downside is that rejected recipients are logged with NOQUEUE instead
       of a mail transaction ID. This complicates the logfile analysis of multi-recipient mail.

       This feature is available in Postfix 2.3 and later.

smtpd_delay_reject (default: yes)
       Wait  until  the   RCPT	 TO   command	before	 evaluating   $smtpd_client_restrictions,
       $smtpd_helo_restrictions  and  $smtpd_sender_restrictions,  or wait until the ETRN command
       before evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.

       This feature is turned on by default because some clients apparently mis-behave	when  the
       Postfix SMTP server rejects commands before RCPT TO.

       The  default  setting  has  one	major benefit: it allows Postfix to log recipient address
       information when rejecting a client name/address or sender address, so that it is possible
       to find out whose mail is being rejected.

smtpd_discard_ehlo_keyword_address_maps (default: empty)
       Lookup  tables,	indexed by the remote SMTP client address, with case insensitive lists of
       EHLO keywords (pipelining, starttls, auth, etc.) that the Postfix  SMTP	server	will  not
       send  in  the  EHLO  response to a remote SMTP client. See smtpd_discard_ehlo_keywords for
       details.  The table is not searched by hostname for robustness reasons.

       This feature is available in Postfix 2.2 and later.

smtpd_discard_ehlo_keywords (default: empty)
       A case insensitive list of EHLO keywords (pipelining, starttls, auth, etc.) that the Post-
       fix SMTP server will not send in the EHLO response to a remote SMTP client.

       This feature is available in Postfix 2.2 and later.

       Notes:

       o      Specify the silent-discard pseudo keyword to prevent this action from being logged.

       o      Use  the	smtpd_discard_ehlo_keyword_address_maps  feature to discard EHLO keywords
	      selectively.

smtpd_end_of_data_restrictions (default: empty)
       Optional access restrictions that the Postfix SMTP server applies in the  context  of  the
       SMTP  END-OF-DATA  command.   See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP
       access restriction lists" for a discussion of evaluation context and time.

       This feature is available in Postfix 2.2 and later.

       See smtpd_data_restrictions for details and limitations.

smtpd_enforce_tls (default: no)
       Mandatory TLS: announce STARTTLS support to remote SMTP clients, and require that  clients
       use TLS encryption.  According to RFC 2487 this MUST NOT be applied in case of a publicly-
       referenced SMTP server.	This option is therefore off by default.

       Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes".

       Note 2: when invoked via "sendmail -bs", Postfix will never offer STARTTLS due to insuffi-
       cient privileges to access the server private key. This is intended behavior.

       This  feature  is  available  in  Postfix  2.2  and  later. With Postfix 2.3 and later use
       smtpd_tls_security_level instead.

smtpd_error_sleep_time (default: 1s)
       With Postfix version 2.1 and later: the SMTP server response delay after a client has made
       more  than  $smtpd_soft_error_limit errors, and fewer than $smtpd_hard_error_limit errors,
       without delivering mail.

       With Postfix version 2.0 and earlier: the SMTP server delay before sending a  reject  (4xx
       or 5xx) response, when the client has made fewer than $smtpd_soft_error_limit errors with-
       out delivering mail.

smtpd_etrn_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the context of a client ETRN
       command.   See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access restriction
       lists" for a discussion of evaluation context and time.

       The Postfix ETRN implementation accepts only destinations that are eligible for the  Post-
       fix "fast flush" service. See the ETRN_README file for details.

       Specify	a  list  of  restrictions,  separated by commas and/or whitespace.  Continue long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The  following  restrictions are specific to the domain name information received with the
       ETRN command.

       check_etrn_access type:table
	      Search the specified access database  for  the  ETRN  domain  name  or  its  parent
	      domains. See the access(5) manual page for details.

       Other restrictions that are valid in this context:

       o      Generic  restrictions that can be used in any SMTP command context, described under
	      smtpd_client_restrictions.

       o      SMTP command specific restrictions described  under  smtpd_client_restrictions  and
	      smtpd_helo_restrictions.

       Example:

       smtpd_etrn_restrictions = permit_mynetworks, reject

smtpd_expansion_filter (default: see postconf -d output)
       What  characters are allowed in $name expansions of RBL reply templates. Characters not in
       the allowed set are replaced by "_".  Use C like escapes  to  specify  special  characters
       such as whitespace.

       This parameter is not subjected to $parameter expansion.

       This feature is available in Postfix 2.0 and later.

smtpd_forbidden_commands (default: CONNECT, GET, POST)
       List  of  commands that cause the Postfix SMTP server to immediately terminate the session
       with a 221 code. This can be used to disconnect clients that obviously  attempt	to  abuse
       the system. In addition to the commands listed in this parameter, commands that follow the
       "Label:" format of message headers will also cause a disconnect.

       This feature is available in Postfix 2.2 and later.

smtpd_hard_error_limit (default: normal: 20, overload: 1)
       The maximal number of errors a remote SMTP client is allowed to	make  without  delivering
       mail. The Postfix SMTP server disconnects when the limit is exceeded. Normally the default
       limit is 20, but it changes under overload to just 1. With Postfix 2.5  and  earlier,  the
       SMTP server always allows up to 20 errors by default.

smtpd_helo_required (default: no)
       Require	that  a remote SMTP client introduces itself with the HELO or EHLO command before
       sending the MAIL command or other commands that require EHLO negotiation.

       Example:

       smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the context of a client HELO
       command.   See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access restriction
       lists" for a discussion of evaluation context and time.

       The default is to permit everything.

       Note: specify "smtpd_helo_required = yes"  to  fully  enforce  this  restriction  (without
       "smtpd_helo_required = yes", a client can simply skip smtpd_helo_restrictions by not send-
       ing HELO or EHLO).

       Specify a list of restrictions, separated by  commas  and/or  whitespace.   Continue  long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The following restrictions are specific to the hostname information received with the HELO
       or EHLO command.

       check_helo_access type:table
	      Search  the  specified  access(5)  database for the HELO or EHLO hostname or parent
	      domains, and execute the corresponding action.  Note: specify  "smtpd_helo_required
	      =  yes"  to  fully enforce this restriction (without "smtpd_helo_required = yes", a
	      client can simply skip check_helo_access by not sending HELO or EHLO).

       check_helo_mx_access type:table
	      Search the specified access(5) database for the MX hosts for the HELO or EHLO host-
	      name,  and  execute  the	corresponding  action.	 Note  1: a result of "OK" is not
	      allowed for safety reasons. Instead, use DUNNO in order to exclude  specific  hosts
	      from blacklists.	Note 2: specify "smtpd_helo_required = yes" to fully enforce this
	      restriction  (without  "smtpd_helo_required  =  yes",  a	client	can  simply  skip
	      check_helo_mx_access  by	not  sending HELO or EHLO).  This feature is available in
	      Postfix 2.1 and later.

       check_helo_ns_access type:table
	      Search the specified access(5) database for the DNS servers for the  HELO  or  EHLO
	      hostname,  and  execute  the corresponding action.  Note 1: a result of "OK" is not
	      allowed for safety reasons. Instead, use DUNNO in order to exclude  specific  hosts
	      from blacklists.	Note 2: specify "smtpd_helo_required = yes" to fully enforce this
	      restriction  (without  "smtpd_helo_required  =  yes",  a	client	can  simply  skip
	      check_helo_ns_access  by	not  sending  HELO or EHLO). This feature is available in
	      Postfix 2.1 and later.

       reject_invalid_helo_hostname (with Postfix < 2.3: reject_invalid_hostname)
	      Reject the request when the HELO or EHLO	hostname  is  malformed.   Note:  specify
	      "smtpd_helo_required   =	 yes"	to   fully   enforce  this  restriction  (without
	      "smtpd_helo_required = yes", a client can simply skip  reject_invalid_helo_hostname
	      by not sending HELO or EHLO).
	      The  invalid_hostname_reject_code specifies the response code for rejected requests
	      (default: 501).

       reject_non_fqdn_helo_hostname (with Postfix < 2.3: reject_non_fqdn_hostname)
	      Reject the request when the HELO or EHLO hostname is not in fully-qualified  domain
	      form,  as  required  by the RFC. Note: specify "smtpd_helo_required = yes" to fully
	      enforce this restriction (without "smtpd_helo_required = yes", a client can  simply
	      skip reject_non_fqdn_helo_hostname by not sending HELO or EHLO).
	      The  non_fqdn_reject_code  parameter  specifies  the  response  code  for  rejected
	      requests (default: 504).

       reject_rhsbl_helo rbl_domain=d.d.d.d
	      Reject the request when the HELO or EHLO hostname hostname is  listed  with  the	A
	      record  "d.d.d.d"  under rbl_domain (Postfix version 2.1 and later only).  Each "d"
	      is a number, or a pattern inside "[]" that contains one or more ";"-separated  num-
	      bers or number..number ranges (Postfix version 2.8 and later).  If no "=d.d.d.d" is
	      specified, reject the request when the HELO or EHLO hostname is listed with  any	A
	      record  under  rbl_domain. See the reject_rbl_client description for additional RBL
	      related configuration parameters.  Note: specify	"smtpd_helo_required  =  yes"  to
	      fully  enforce  this restriction (without "smtpd_helo_required = yes", a client can
	      simply skip reject_rhsbl_helo by not sending HELO or EHLO). This feature is  avail-
	      able in Postfix 2.0 and later.

       reject_unknown_helo_hostname (with Postfix < 2.3: reject_unknown_hostname)
	      Reject the request when the HELO or EHLO hostname has no DNS A or MX record.
	      The  unknown_hostname_reject_code  parameter  specifies the numerical response code
	      for rejected requests (default: 450).
	      The unknown_helo_hostname_tempfail_action parameter specifies the  action  after	a
	      temporary  DNS error (default: defer_if_permit). Note: specify "smtpd_helo_required
	      = yes" to fully enforce this restriction (without "smtpd_helo_required  =  yes",	a
	      client can simply skip reject_unknown_helo_hostname by not sending HELO or EHLO).

       Other restrictions that are valid in this context:

       o      Generic  restrictions that can be used in any SMTP command context, described under
	      smtpd_client_restrictions.

       o      Client  hostname	or  network  address  specific	 restrictions	described   under
	      smtpd_client_restrictions.

       o      SMTP  command  specific  restrictions  described under smtpd_sender_restrictions or
	      smtpd_recipient_restrictions.  When sender or  recipient	restrictions  are  listed
	      under  smtpd_helo_restrictions,  they  have  effect only with "smtpd_delay_reject =
	      yes", so that $smtpd_helo_restrictions is evaluated at the time of the RCPT TO com-
	      mand.

       Examples:

       smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
       smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname

smtpd_history_flush_threshold (default: 100)
       The  maximal  number  of  lines	in  the  Postfix SMTP server command history before it is
       flushed upon receipt of EHLO, RSET, or end of DATA.

smtpd_junk_command_limit (default: normal: 100, overload: 1)
       The number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote SMTP client can  send
       before  the  Postfix SMTP server starts to increment the error counter with each junk com-
       mand.   The  junk  command  count  is  reset  after  mail  is  delivered.   See	also  the
       smtpd_error_sleep_time  and smtpd_soft_error_limit configuration parameters.  Normally the
       default limit is 100, but it changes under overload to just 1. With Postfix 2.5	and  ear-
       lier, the SMTP server always allows up to 100 junk commands by default.

smtpd_log_access_permit_actions (default: empty)
       Enable  logging of the named "permit" actions in SMTP server access lists (by default, the
       SMTP server logs "reject" actions but not "permit" actions).  This feature does not affect
       conditional actions such as "defer_if_permit".

       Specify	a list of "permit" action names, "/file/name" or "type:table" patterns, separated
       by commas and/or whitespace. The list is matched left to right, and the	search	stops  on
       the first match. A "/file/name" pattern is replaced by its contents; a "type:table" lookup
       table is matched when a name matches a lookup key (the lookup result  is  ignored).   Con-
       tinue  long lines by starting the next line with whitespace. Specify "!pattern" to exclude
       a name from the list.

       Examples:

       /etc/postfix/main.cf:
	   # Log all "permit" actions.
	   smtpd_log_access_permit_actions = static:all

       /etc/postfix/main.cf:
	   # Log "permit_dnswl_client" only.
	   smtpd_log_access_permit_actions = permit_dnswl_client

       This feature is available in Postfix 2.10 and later.

smtpd_milters (default: empty)
       A list of Milter (mail filter) applications for new mail  that  arrives	via  the  Postfix
       smtpd(8)  server.  Specify space or comma as separator. See the MILTER_README document for
       details.

       This feature is available in Postfix 2.3 and later.

smtpd_noop_commands (default: empty)
       List of commands that the Postfix SMTP server replies to with "250 Ok", without doing  any
       syntax checks and without changing state.  This list overrides any commands built into the
       Postfix SMTP server.

smtpd_null_access_lookup_key (default: <>)
       The lookup key to be used in SMTP access(5) tables instead of the null sender address.

smtpd_peername_lookup (default: yes)
       Attempt to look up the remote SMTP client hostname, and verify that the name  matches  the
       client  IP address. A client name is set to "unknown" when it cannot be looked up or veri-
       fied, or when name lookup is disabled.  Turning off name lookup reduces delays due to  DNS
       lookup and increases the maximal inbound delivery rate.

       This feature is available in Postfix 2.3 and later.

smtpd_per_record_deadline (default: normal: no, overload: yes)
       Change  the  behavior of the smtpd_timeout time limit, from a time limit per read or write
       system call, to a time limit to send or receive a complete record (an SMTP  command  line,
       SMTP  response line, SMTP message content line, or TLS protocol message).  This limits the
       impact from hostile peers that trickle data one byte at a time.

       Note: when per-record deadlines are enabled, a short timeout may cause problems	with  TLS
       over very slow network connections.  The reasons are that a TLS protocol message can be up
       to 16 kbytes long (with TLSv1), and that an entire TLS protocol message must  be  sent  or
       received within the per-record deadline.

       This  feature  is  available  in  Postfix  2.9 and later. With older Postfix releases, the
       behavior is as if this parameter is set to "no".

smtpd_policy_service_max_idle (default: 300s)
       The time after which an idle SMTPD policy service connection is closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_max_ttl (default: 1000s)
       The time after which an active SMTPD policy service connection is closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_timeout (default: 100s)
       The time limit for connecting to, writing to or receiving from a  delegated  SMTPD  policy
       server.

       This feature is available in Postfix 2.1 and later.

smtpd_proxy_ehlo (default: $myhostname)
       How the Postfix SMTP server announces itself to the proxy filter.  By default, the Postfix
       hostname is used.

       This feature is available in Postfix 2.1 and later.

smtpd_proxy_filter (default: empty)
       The hostname and TCP port of the mail filtering proxy server.  The proxy receives all mail
       from  the  Postfix SMTP server, and is supposed to give the result to another Postfix SMTP
       server process.

       Specify "host:port" or "inet:host:port" for a TCP endpoint, or "unix:pathname" for a UNIX-
       domain  endpoint.  The host can be specified as an IP address or as a symbolic name; no MX
       lookups are done.  When no "host" or "host:"  are specified, the local machine is assumed.
       Pathname interpretation is relative to the Postfix queue directory.

       This feature is available in Postfix 2.1 and later.

       The "inet:" and "unix:" prefixes are available in Postfix 2.3 and later.

smtpd_proxy_options (default: empty)
       List  of options that control how the Postfix SMTP server communicates with a before-queue
       content filter. Specify zero or more of the following, separated by comma or whitespace.

       speed_adjust
	      Do not connect to a before-queue content filter until an entire  message	has  been
	      received.  This reduces the number of simultaneous before-queue content filter pro-
	      cesses.

       NOTE 1: A filter must not selectively reject  recipients  of  a	multi-recipient  message.
       Rejecting all recipients is OK, as is accepting all recipients.

       NOTE  2:  This  feature	increases  the	minimum  amount  of  free  queue  space  by $mes-
       sage_size_limit. The extra space is needed to save the message to a temporary file.

       This feature is available in Postfix 2.7 and later.

smtpd_proxy_timeout (default: 100s)
       The time limit for connecting to a proxy filter and for sending or receiving  information.
       When a connection fails the client gets a generic error message while more detailed infor-
       mation is logged to the maillog file.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_recipient_limit (default: 1000)
       The maximal number of recipients that the Postfix SMTP server accepts per message delivery
       request.

smtpd_recipient_overshoot_limit (default: 1000)
       The number of recipients that a remote SMTP client can send in excess of the limit  speci-
       fied  with  $smtpd_recipient_limit, before the Postfix SMTP server increments the per-ses-
       sion error count for each excess recipient.

smtpd_recipient_restrictions (default: see postconf -d output)
       Optional restrictions that the Postfix SMTP server applies in the context of a client RCPT
       TO  command,  after  smtpd_relay_restrictions.	See SMTPD_ACCESS_README, section "Delayed
       evaluation of SMTP access restriction lists" for a discussion of  evaluation  context  and
       time.

       With  Postfix  versions before 2.10, the rules for relay permission and spam blocking were
       combined under smtpd_recipient_restrictions, resulting in error-prone  configuration.   As
       of    Postfix   2.10,   relay   permission   rules   are   preferably   implemented   with
       smtpd_relay_restrictions, so that a permissive spam blocking  policy  under  smtpd_recipi-
       ent_restrictions will no longer result in a permissive mail relay policy.

       For  backwards compatibility, sites that migrate from Postfix versions before 2.10 can set
       smtpd_relay_restrictions to the empty value, and use smtpd_recipient_restrictions  exactly
       as before.

       IMPORTANT: Either the smtpd_relay_restrictions or the smtpd_recipient_restrictions parame-
       ter must specify at least one of the following restrictions. Otherwise Postfix will refuse
       to receive mail:

	   reject, reject_unauth_destination

	   defer, defer_if_permit, defer_unauth_destination

       Specify	a  list  of  restrictions,  separated by commas and/or whitespace.  Continue long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The following restrictions are specific to the recipient address that is received with the
       RCPT TO command.

       check_recipient_access type:table
	      Search the specified access(5) database for the resolved RCPT TO	address,  domain,
	      parent domains, or localpart@, and execute the corresponding action.

       check_recipient_mx_access type:table
	      Search  the  specified  access(5) database for the MX hosts for the RCPT TO domain,
	      and execute the corresponding action.  Note: a result of "OK" is	not  allowed  for
	      safety  reasons.	Instead, use DUNNO in order to exclude specific hosts from black-
	      lists.  This feature is available in Postfix 2.1 and later.

       check_recipient_ns_access type:table
	      Search the specified access(5) database for the DNS servers for the RCPT TO domain,
	      and  execute  the  corresponding action.	Note: a result of "OK" is not allowed for
	      safety reasons. Instead, use DUNNO in order to exclude specific hosts  from  black-
	      lists.  This feature is available in Postfix 2.1 and later.

       permit_auth_destination
	      Permit the request when one of the following is true:

       o      Postfix  is mail forwarder: the resolved RCPT TO domain matches $relay_domains or a
	      subdomain thereof, and the address contains no sender-specified routing (user@else-
	      where@domain),

       o      Postfix  is  the final destination: the resolved RCPT TO domain matches $mydestina-
	      tion,  $inet_interfaces,	$proxy_interfaces,   $virtual_alias_domains,   or   $vir-
	      tual_mailbox_domains,   and   the  address  contains  no	sender-specified  routing
	      (user@elsewhere@domain).

       permit_mx_backup
	      Permit the request when the local mail system is backup MX for the RCPT TO  domain,
	      or  when	the  domain is an authorized destination (see permit_auth_destination for
	      definition).

       o      Safety: permit_mx_backup does not accept addresses that have sender-specified rout-
	      ing information (example: user@elsewhere@domain).

       o      Safety: permit_mx_backup can be vulnerable to mis-use when access is not restricted
	      with permit_mx_backup_networks.

       o      Safety: as of Postfix version 2.3, permit_mx_backup no longer accepts  the  address
	      when the local mail system is primary MX for the recipient domain.  Exception: per-
	      mit_mx_backup accepts the address when it specifies an authorized destination  (see
	      permit_auth_destination for definition).

       o      Limitation:  mail  may  be  rejected in case of a temporary DNS lookup problem with
	      Postfix prior to version 2.0.

       reject_non_fqdn_recipient
	      Reject the request when the RCPT TO address is not in fully-qualified domain  form,
	      as required by the RFC.
	      The  non_fqdn_reject_code  parameter  specifies  the  response  code  for  rejected
	      requests (default: 504).

       reject_rhsbl_recipient rbl_domain=d.d.d.d
	      Reject the request when the RCPT TO domain is listed with the  A	record	"d.d.d.d"
	      under  rbl_domain (Postfix version 2.1 and later only).  Each "d" is a number, or a
	      pattern inside "[]" that contains one or more ";"-separated numbers or number..num-
	      ber  ranges  (Postfix version 2.8 and later). If no "=d.d.d.d" is specified, reject
	      the request when the RCPT TO domain is listed with any A record under rbl_domain.
	      The  maps_rbl_reject_code  parameter  specifies  the  response  code  for  rejected
	      requests	(default:  554);  the  default_rbl_reply  parameter specifies the default
	      server reply; and the rbl_reply_maps parameter specifies tables with server replies
	      indexed by rbl_domain.  This feature is available in Postfix version 2.0 and later.

       reject_unauth_destination
	      Reject the request unless one of the following is true:

       o      Postfix  is mail forwarder: the resolved RCPT TO domain matches $relay_domains or a
	      subdomain  thereof,  and	 contains   no	 sender-specified   routing   (user@else-
	      where@domain),

       o      Postfix  is  the final destination: the resolved RCPT TO domain matches $mydestina-
	      tion,  $inet_interfaces,	$proxy_interfaces,   $virtual_alias_domains,   or   $vir-
	      tual_mailbox_domains,   and   contains   no  sender-specified  routing  (user@else-
	      where@domain).
	      The relay_domains_reject_code parameter specifies the response  code  for  rejected
	      requests (default: 554).

       defer_unauth_destination
	      Reject  the  same requests as reject_unauth_destination, with a non-permanent error
	      code.  This feature is available in Postfix 2.10 and later.

       reject_unknown_recipient_domain
	      Reject the request when Postfix is not final destination for the recipient  domain,
	      and  the	RCPT  TO  domain has 1) no DNS A or MX record or 2) a malformed MX record
	      such as a record with a zero-length MX hostname (Postfix version 2.3 and later).
	      The unknown_address_reject_code parameter specifies the numerical response code for
	      rejected	requests  (default: 450).  The response is always 450 in case of a tempo-
	      rary DNS error.
	      The unknown_address_tempfail_action parameter specifies the action after	a  tempo-
	      rary DNS error (default: defer_if_permit).

       reject_unlisted_recipient (with Postfix version 2.0: check_recipient_maps)
	      Reject  the  request  when  the  RCPT TO address is not listed in the list of valid
	      recipients for its domain class. See the smtpd_reject_unlisted_recipient	parameter
	      description for details.	This feature is available in Postfix 2.1 and later.

       reject_unverified_recipient
	      Reject the request when mail to the RCPT TO address is known to bounce, or when the
	      recipient address destination is not reachable.  Address	verification  information
	      is  managed  by  the verify(8) server; see the ADDRESS_VERIFICATION_README file for
	      details.
	      The unverified_recipient_reject_code parameter  specifies  the  numerical  response
	      code when an address is known to bounce (default: 450, change into 550 when you are
	      confident that it is safe to do so).
	      The unverified_recipient_defer_code parameter specifies the numerical response code
	      when an address probe failed due to a temporary problem (default: 450).
	      The  unverified_recipient_tempfail_action  parameter  specifies  the  action  after
	      addres probe failure due to a temporary problem (default: defer_if_permit).
	      This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       o      Generic restrictions that can be used in any SMTP command context, described  under
	      smtpd_client_restrictions.

       o      SMTP  command  specific  restrictions  described	under  smtpd_client_restrictions,
	      smtpd_helo_restrictions and smtpd_sender_restrictions.

       Example:

       # The Postfix before 2.10 default mail relay policy. Later Postfix
       # versions implement this preferably with smtpd_relay_restrictions.
       smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

smtpd_reject_footer (default: empty)
       Optional information that is appended after each Postfix SMTP server 4XX or 5XX response.

       The following example uses "\c" at the start of the template (supported	in  Postfix  2.10
       and  later)  to	suppress  the line break between the reply text and the footer text. With
       earlier Postfix versions, the footer text always begins on a new line,  and  the  "\c"  is
       output literally.

       /etc/postfix/main.cf:
	   smtpd_reject_footer = \c. For assistance, call 800-555-0101.
	    Please provide the following information in your problem report:
	    time ($localtime), client ($client_address) and server
	    ($server_name).

       Server response:

	   550-5.5.1 <user@example> Recipient address rejected: User
	   unknown. For assistance, call 800-555-0101. Please provide the
	   following information in your problem report: time (Jan 4 15:42:00),
	   client (192.168.1.248) and server (mail1.example.com).

       Note:  the above text is meant to make it easier to find the Postfix logfile records for a
       failed SMTP session. The text itself is not logged to the Postfix  SMTP	server's  maillog
       file.

       Be  sure  to  keep  the text as short as possible. Long text may be truncated before it is
       logged to the remote SMTP client's maillog file, or before it is returned to the sender in
       a delivery status notification.

       This  feature  supports a limited number of $name attributes in the footer text. These are
       replaced by their current value for the SMTP session:

       client_address
	      The Client IP address that is logged in the maillog file.

       client_port
	      The client TCP port that is logged in the maillog file.

       localtime
	      The server local time (Mmm dd hh:mm:ss) that is logged in the maillog file.

       server_name
	      The server's myhostname value.  This attribute is made  available  for  sites  with
	      multiple	MTAs (perhaps behind a load-balancer), where the server name can help the
	      server support team to quickly find the right log files.

       Notes:

       o      NOT SUPPORTED are other attributes such as sender, recipient,  or  main.cf  parame-
	      ters.

       o      For safety reasons, text that does not match $smtpd_expansion_filter is censored.

       This  feature  supports the two-character sequence \n as a request for a line break in the
       footer text. Postfix automatically inserts after each  line  break  the	three-digit  SMTP
       reply code (and optional enhanced status code) from the original Postfix reject message.

       To  work around mail software that mis-handles multi-line replies, specify the two-charac-
       ter sequence \c at the start of the template.  This suppresses the line break between  the
       reply text and the footer text (Postfix 2.10 and later).

       This feature is available in Postfix 2.8 and later.

smtpd_reject_unlisted_recipient (default: yes)
       Request	that  the  Postfix SMTP server rejects mail for unknown recipient addresses, even
       when no explicit reject_unlisted_recipient access restriction is specified. This  prevents
       the Postfix queue from filling up with undeliverable MAILER-DAEMON messages.

       An  address  is	always considered "known" when it matches a virtual(5) alias or a canoni-
       cal(5) mapping.

       o      The recipient domain matches $mydestination, $inet_interfaces or $proxy_interfaces,
	      but the recipient is not listed in $local_recipient_maps, and $local_recipient_maps
	      is not null.

       o      The recipient domain matches $virtual_alias_domains but the recipient is not listed
	      in $virtual_alias_maps.

       o      The  recipient  domain  matches  $virtual_mailbox_domains  but the recipient is not
	      listed in $virtual_mailbox_maps, and $virtual_mailbox_maps is not null.

       o      The recipient domain matches $relay_domains but the  recipient  is  not  listed  in
	      $relay_recipient_maps, and $relay_recipient_maps is not null.

       This feature is available in Postfix 2.1 and later.

smtpd_reject_unlisted_sender (default: no)
       Request that the Postfix SMTP server rejects mail from unknown sender addresses, even when
       no explicit reject_unlisted_sender access restriction is specified. This can slow down  an
       explosion of forged mail from worms or viruses.

       An  address  is	always considered "known" when it matches a virtual(5) alias or a canoni-
       cal(5) mapping.

       o      The sender domain matches $mydestination,  $inet_interfaces  or  $proxy_interfaces,
	      but the sender is not listed in $local_recipient_maps, and $local_recipient_maps is
	      not null.

       o      The sender domain matches $virtual_alias_domains but the sender is  not  listed  in
	      $virtual_alias_maps.

       o      The  sender domain matches $virtual_mailbox_domains but the sender is not listed in
	      $virtual_mailbox_maps, and $virtual_mailbox_maps is not null.

       o      The  sender  domain  matches  $relay_domains  but  the  sender  is  not  listed  in
	      $relay_recipient_maps, and $relay_recipient_maps is not null.

       This feature is available in Postfix 2.1 and later.

smtpd_relay_restrictions       (default:       permit_mynetworks,      permit_sasl_authenticated,
       defer_unauth_destination)
       Access restrictions for mail relay control that the Postfix SMTP  server  applies  in  the
       context	  of   the   RCPT   TO	 command,   before   smtpd_recipient_restrictions.    See
       SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access restriction lists"  for	a
       discussion of evaluation context and time.

       With  Postfix  versions before 2.10, the rules for relay permission and spam blocking were
       combined under smtpd_recipient_restrictions, resulting in error-prone  configuration.   As
       of    Postfix   2.10,   relay   permission   rules   are   preferably   implemented   with
       smtpd_relay_restrictions, so that a permissive spam blocking  policy  under  smtpd_recipi-
       ent_restrictions will no longer result in a permissive mail relay policy.

       For  backwards compatibility, sites that migrate from Postfix versions before 2.10 can set
       smtpd_relay_restrictions to the empty value, and use smtpd_recipient_restrictions  exactly
       as before.

       By default, the Postfix SMTP server accepts:

       o      Mail from clients whose IP address matches $mynetworks, or:

       o      Mail  to	remote	destinations that match $relay_domains, except for addresses that
	      contain sender-specified routing (user@elsewhere@domain), or:

       o      Mail to  local  destinations  that  match  $inet_interfaces  or  $proxy_interfaces,
	      $mydestination, $virtual_alias_domains, or $virtual_mailbox_domains.

       IMPORTANT: Either the smtpd_relay_restrictions or the smtpd_recipient_restrictions parame-
       ter must specify at least one of the following restrictions. Otherwise Postfix will refuse
       to receive mail:

	   reject, reject_unauth_destination

	   defer, defer_if_permit, defer_unauth_destination

       Specify	a  list  of  restrictions,  separated by commas and/or whitespace.  Continue long
       lines by starting the next line with whitespace.  The same restrictions are  available  as
       documented under smtpd_recipient_restrictions.

       This feature is available in Postix 2.10 and later.

smtpd_restriction_classes (default: empty)
       User-defined  aliases  for  groups of access restrictions. The aliases can be specified in
       smtpd_recipient_restrictions etc., and on the right-hand side of a Postfix  access(5)  ta-
       ble.

       One  major  application	is  for implementing per-recipient UCE control.  See the RESTRIC-
       TION_CLASS_README document for other examples.

smtpd_sasl_application_name (default: smtpd)
       The application name that the Postfix SMTP server uses  for  SASL  server  initialization.
       This  controls the name of the SASL configuration file. The default value is smtpd, corre-
       sponding to a SASL configuration file named smtpd.conf.

       This feature is available in Postfix 2.1 and 2.2. With  Postfix	2.3  it  was  renamed  to
       smtpd_sasl_path.

smtpd_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix SMTP server. By default, the Postfix SMTP server
       does not use authentication.

       If a remote SMTP client is authenticated, the permit_sasl_authenticated access restriction
       can be used to permit relay access, like this:

	   # With Postfix 2.10 and later, the mail relay policy is
	   # preferably specified under smtpd_relay_restrictions.
	   smtpd_relay_restrictions =
	       permit_mynetworks, permit_sasl_authenticated, ...

       # With Postfix before 2.10, the relay policy can be
       # specified only under smtpd_recipient_restrictions.
       smtpd_recipient_restrictions =
	   permit_mynetworks, permit_sasl_authenticated, ...

       To reject all SMTP connections from unauthenticated clients, specify "smtpd_delay_reject =
       yes" (which is the default) and use:

	   smtpd_client_restrictions = permit_sasl_authenticated, reject

       See the SASL_README file for SASL configuration and operation details.

smtpd_sasl_authenticated_header (default: no)
       Report the SASL authenticated user name in the smtpd(8) Received message header.

       This feature is available in Postfix 2.3 and later.

smtpd_sasl_exceptions_networks (default: empty)
       What remote SMTP clients the Postfix SMTP server will not offer AUTH support to.

       Some clients (Netscape 4 at least) have a bug that causes them  to  require  a  login  and
       password  whenever  AUTH  is  offered, whether it's necessary or not. To work around this,
       specify, for example, $mynetworks to prevent Postfix from offering AUTH to local clients.

       Specify a list of network/netmask patterns, separated by  commas  and/or  whitespace.  The
       mask  specifies	the  number  of  bits in the network part of a host address. You can also
       "/file/name" or "type:table" patterns.  A "/file/name" pattern is  replaced  by	its  con-
       tents;  a  "type:table" lookup table is matched when a table entry matches a lookup string
       (the lookup result is ignored).	Continue long lines by starting the next line with white-
       space.  Specify "!pattern" to exclude an address or network block from the list.  The form
       "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:  IP  version  6  address  information  must  be   specified   inside   []	 in   the
       smtpd_sasl_exceptions_networks  value,  and in files specified with "/file/name".  IP ver-
       sion 6 addresses contain the ":"  character,  and  would  otherwise  be	confused  with	a
       "type:table" pattern.

       Example:

       smtpd_sasl_exceptions_networks = $mynetworks

       This feature is available in Postfix 2.1 and later.

smtpd_sasl_local_domain (default: empty)
       The name of the Postfix SMTP server's local SASL authentication realm.

       By default, the local authentication realm name is the null string.

       Examples:

       smtpd_sasl_local_domain = $mydomain
       smtpd_sasl_local_domain = $myhostname

smtpd_sasl_path (default: smtpd)
       Implementation-specific	information  that  the	Postfix SMTP server passes through to the
       SASL plug-in implementation that is selected with smtpd_sasl_type.  Typically this  speci-
       fies the name of a configuration file or rendezvous point.

       This  feature  is  available  in  Postfix 2.3 and later. In earlier releases it was called
       smtpd_sasl_application_name.

smtpd_sasl_security_options (default: noanonymous)
       Postfix SMTP server SASL security options; as of Postfix 2.3 the list  of  available  fea-
       tures depends on the SASL server implementation that is selected with smtpd_sasl_type.

       The following security features are defined for the cyrus server SASL implementation:

       Restrict  what authentication mechanisms the Postfix SMTP server will offer to the client.
       The list of available authentication mechanisms is system dependent.

       Specify zero or more of the following:

       noplaintext
	      Disallow methods that use plaintext passwords.

       noactive
	      Disallow methods subject to active (non-dictionary) attack.

       nodictionary
	      Disallow methods subject to passive (dictionary) attack.

       noanonymous
	      Disallow methods that allow anonymous authentication.

       forward_secrecy
	      Only allow methods that support forward secrecy (Dovecot only).

       mutual_auth
	      Only allow methods that provide mutual authentication  (not  available  with  Cyrus
	      SASL version 1).

       By default, the Postfix SMTP server accepts plaintext passwords but not anonymous logins.

       Warning:  it appears that clients try authentication methods in the order as advertised by
       the server (e.g., PLAIN ANONYMOUS CRAM-MD5) which means	that  if  you  disable	plaintext
       passwords, clients will log in anonymously, even when they should be able to use CRAM-MD5.
       So, if you disable plaintext logins, disable anonymous logins too.  Postfix treats  anony-
       mous login as no authentication.

       Example:

       smtpd_sasl_security_options = noanonymous, noplaintext

smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options)
       The  SASL  authentication  security  options  that  the	Postfix  SMTP server uses for TLS
       encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtpd_sasl_type (default: cyrus)
       The SASL plug-in type that the Postfix SMTP server  should  use	for  authentication.  The
       available types are listed with the "postconf -a" command.

       This feature is available in Postfix 2.3 and later.

smtpd_sender_login_maps (default: empty)
       Optional lookup table with the SASL login names that own sender (MAIL FROM) addresses.

       Specify	zero  or more "type:table" lookup tables. With lookups from indexed files such as
       DB or DBM, or from networked tables such as NIS, LDAP or SQL, the following search  opera-
       tions are done with a sender address of user@domain:

       1) user@domain
	      This table lookup is always done and has the highest precedence.

       2) user
	      This  table  lookup is done only when the domain part of the sender address matches
	      $myorigin, $mydestination, $inet_interfaces or $proxy_interfaces.

       3) @domain
	      This table lookup is done last and has the lowest precedence.

       In all cases the result of table lookup must be either "not found" or a list of SASL login
       names separated by comma and/or whitespace.

smtpd_sender_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the context of a client MAIL
       FROM command.   See  SMTPD_ACCESS_README,  section  "Delayed  evaluation  of  SMTP  access
       restriction lists" for a discussion of evaluation context and time.

       The default is to permit everything.

       Specify	a  list  of  restrictions,  separated by commas and/or whitespace.  Continue long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The  following restrictions are specific to the sender address received with the MAIL FROM
       command.

       check_sender_access type:table
	      Search the specified access(5) database for the MAIL FROM address,  domain,  parent
	      domains, or localpart@, and execute the corresponding action.

       check_sender_mx_access type:table
	      Search the specified access(5) database for the MX hosts for the MAIL FROM address,
	      and execute the corresponding action.  Note: a result of "OK" is	not  allowed  for
	      safety  reasons.	Instead, use DUNNO in order to exclude specific hosts from black-
	      lists.  This feature is available in Postfix 2.1 and later.

       check_sender_ns_access type:table
	      Search the specified access(5) database for the  DNS  servers  for  the  MAIL  FROM
	      address,	and  execute  the  corresponding  action.   Note: a result of "OK" is not
	      allowed for safety reasons. Instead, use DUNNO in order to exclude  specific  hosts
	      from blacklists.	This feature is available in Postfix 2.1 and later.

       reject_authenticated_sender_login_mismatch
	      Enforces	the  reject_sender_login_mismatch  restriction	for authenticated clients
	      only. This feature is available in Postfix version 2.1 and later.

       reject_non_fqdn_sender
	      Reject the request when the MAIL FROM address  is  not  in  fully-qualified  domain
	      form, as required by the RFC.
	      The  non_fqdn_reject_code  parameter  specifies  the  response  code  for  rejected
	      requests (default: 504).

       reject_rhsbl_sender rbl_domain=d.d.d.d
	      Reject the request when the MAIL FROM domain is listed with the A record	"d.d.d.d"
	      under  rbl_domain (Postfix version 2.1 and later only).  Each "d" is a number, or a
	      pattern inside "[]" that contains one or more ";"-separated numbers or number..num-
	      ber  ranges  (Postfix version 2.8 and later). If no "=d.d.d.d" is specified, reject
	      the request when the MAIL FROM domain is listed with any A record under rbl_domain.
	      The  maps_rbl_reject_code  parameter  specifies  the  response  code  for  rejected
	      requests	(default:   554);  the	default_rbl_reply parameter specifies the default
	      server reply; and the rbl_reply_maps parameter specifies tables with server replies
	      indexed by rbl_domain.  This feature is available in Postfix 2.0 and later.

       reject_sender_login_mismatch
	      Reject  the  request  when $smtpd_sender_login_maps specifies an owner for the MAIL
	      FROM address, but the client is not (SASL) logged in  as	that  MAIL  FROM  address
	      owner;  or  when	the client is (SASL) logged in, but the client login name doesn't
	      own the MAIL FROM address according to $smtpd_sender_login_maps.

       reject_unauthenticated_sender_login_mismatch
	      Enforces the reject_sender_login_mismatch restriction for  unauthenticated  clients
	      only. This feature is available in Postfix version 2.1 and later.

       reject_unknown_sender_domain
	      Reject  the  request  when Postfix is not final destination for the sender address,
	      and the MAIL FROM domain has 1) no DNS A or MX record, or 2) a malformed MX  record
	      such as a record with a zero-length MX hostname (Postfix version 2.3 and later).
	      The unknown_address_reject_code parameter specifies the numerical response code for
	      rejected requests (default: 450).  The response is always 450 in case of	a  tempo-
	      rary DNS error.
	      The  unknown_address_tempfail_action  parameter specifies the action after a tempo-
	      rary DNS error (default: defer_if_permit).

       reject_unlisted_sender
	      Reject the request when the MAIL FROM address is not listed in the  list	of  valid
	      recipients  for  its  domain  class. See the smtpd_reject_unlisted_sender parameter
	      description for details.	This feature is available in Postfix 2.1 and later.

       reject_unverified_sender
	      Reject the request when mail to the MAIL FROM address is known to bounce,  or  when
	      the  sender address destination is not reachable.  Address verification information
	      is managed by the verify(8) server; see the  ADDRESS_VERIFICATION_README	file  for
	      details.
	      The  unverified_sender_reject_code  parameter specifies the numerical response code
	      when an address is known to bounce (default: 450, change into 550 when you are con-
	      fident that it is safe to do so).
	      The  unverified_sender_defer_code  specifies  the  numerical  response code when an
	      address address probe failed due to a temporary problem (default: 450).
	      The unverified_sender_tempfail_action parameter specifies the action after  address
	      probe failure due to a temporary problem (default: defer_if_permit).
	      This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       o      Generic  restrictions that can be used in any SMTP command context, described under
	      smtpd_client_restrictions.

       o      SMTP command specific restrictions described  under  smtpd_client_restrictions  and
	      smtpd_helo_restrictions.

       o      SMTP  command  specific  restrictions described under smtpd_recipient_restrictions.
	      When recipient restrictions are listed under smtpd_sender_restrictions,  they  have
	      effect  only with "smtpd_delay_reject = yes", so that $smtpd_sender_restrictions is
	      evaluated at the time of the RCPT TO command.

       Examples:

       smtpd_sender_restrictions = reject_unknown_sender_domain
       smtpd_sender_restrictions = reject_unknown_sender_domain,
	   check_sender_access hash:/etc/postfix/access

smtpd_service_name (default: smtpd)
       The internal service that postscreen(8) hands off allowed connections to. In a future ver-
       sion there may be different classes of SMTP service.

       This feature is available in Postfix 2.8.

smtpd_soft_error_limit (default: 10)
       The  number  of	errors	a  remote  SMTP client is allowed to make without delivering mail
       before the Postfix SMTP server slows down all its responses.

       o      With Postfix version 2.1 and later, the Postfix SMTP server delays all responses by
	      $smtpd_error_sleep_time seconds.

       o      With Postfix versions 2.0 and earlier, the Postfix SMTP server delays all responses
	      by (number of errors) seconds.

smtpd_starttls_timeout (default: see postconf -d output)
       The time limit for Postfix SMTP server write and read operations during	TLS  startup  and
       shutdown handshake procedures. The current default value is stress-dependent. Before Post-
       fix version 2.8, it was fixed at 300s.

       This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: normal: 300s, overload: 10s)
       The time limit for sending a Postfix SMTP server response and for receiving a remote  SMTP
       client  request. Normally the default limit is 300s, but it changes under overload to just
       10s. With Postfix 2.5 and earlier, the SMTP server always uses a time  limit  of  300s  by
       default.

       Note:  if  you set SMTP time limits to very large values you may have to update the global
       ipc_timeout parameter.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtpd_tls_CAfile (default: empty)
       A  file	containing (PEM format) CA certificates of root CAs trusted to sign either remote
       SMTP client certificates or intermediate CA certificates.  These are  loaded  into  memory
       before  the  smtpd(8)  server  enters  the  chroot jail. If the number of trusted roots is
       large, consider using smtpd_tls_CApath instead, but note that the latter directory must be
       present	in the chroot jail if the smtpd(8) server is chrooted. This file may also be used
       to augment the server certificate trust chain, but it is best to include all the  required
       certificates directly in the server certificate file.

       Specify	"smtpd_tls_CAfile  =  /path/to/system_CA_file"	to  use  ONLY the system-supplied
       default certificate authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending the system-supplied
       default CAs and trusting third-party certificates.

       By   default  (see  smtpd_tls_ask_ccert),  client  certificates	are  not  requested,  and
       smtpd_tls_CAfile should remain empty. If you do make use of client certificates, the  dis-
       tinguished  names (DNs) of the certificate authorities listed in smtpd_tls_CAfile are sent
       to the remote SMTP client in the client certificate request message.  MUAs  with  multiple
       client  certificates  may  use the list of preferred certificate authorities to select the
       correct client certificate.  You may want to put your "preferred" CA or CAs in this  file,
       and install other trusted CAs in $smtpd_tls_CApath.

       Example:

       smtpd_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_CApath (default: empty)
       A  directory  containing  (PEM  format) CA certificates of root CAs trusted to sign either
       remote SMTP client certificates or intermediate CA certificates. Do not forget  to  create
       the  necessary  "hash"  links  with,  for  example, "$OPENSSL_HOME/bin/c_rehash /etc/post-
       fix/certs". To use smtpd_tls_CApath in chroot mode, this directory (or  a  copy)  must  be
       inside the chroot jail.

       Specify	"smtpd_tls_CApath = /path/to/system_CA_directory" to use ONLY the system-supplied
       default certificate authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending the system-supplied
       default CAs and trusting third-party certificates.

       By   default  (see  smtpd_tls_ask_ccert),  client  certificates	are  not  requested,  and
       smtpd_tls_CApath should remain empty. In contrast to smtpd_tls_CAfile, DNs of  certificate
       authorities  installed  in  $smtpd_tls_CApath  are  not included in the client certificate
       request message. MUAs with multiple client certificates may use the list of preferred cer-
       tificate  authorities  to select the correct client certificate.  You may want to put your
       "preferred" CA or CAs in $smtpd_tls_CAfile, and	install  the  remaining  trusted  CAs  in
       $smtpd_tls_CApath.

       Example:

       smtpd_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtpd_tls_always_issue_session_ids (default: yes)
       Force  the Postfix SMTP server to issue a TLS session id, even when TLS session caching is
       turned off (smtpd_tls_session_cache_database is empty). This behavior is  compatible  with
       Postfix < 2.3.

       With  Postfix 2.3 and later the Postfix SMTP server can disable session id generation when
       TLS session caching is turned off. This keeps remote SMTP clients  from	caching  sessions
       that almost certainly cannot be re-used.

       By  default, the Postfix SMTP server always generates TLS session ids. This works around a
       known defect in mail client applications such as MS Outlook, and may also prevent interop-
       erability issues with other MTAs.

       Example:

       smtpd_tls_always_issue_session_ids = no

       This feature is available in Postfix 2.3 and later.

smtpd_tls_ask_ccert (default: no)
       Ask a remote SMTP client for a client certificate. This information is needed for certifi-
       cate based mail relaying with, for example, the permit_tls_clientcerts feature.

       Some clients such as Netscape will either complain if no certificate is available (for the
       list  of  CAs  in  $smtpd_tls_CAfile) or will offer multiple client certificates to choose
       from. This may be annoying, so this option is "off" by default.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_auth_only (default: no)
       When TLS encryption is optional in the Postfix SMTP server, do not announce or accept SASL
       authentication over unencrypted connections.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_ccert_verifydepth (default: 9)
       The  verification depth for remote SMTP client certificates. A depth of 1 is sufficient if
       the issuing CA is listed in a local CA file.

       The default verification depth is 9 (the OpenSSL default) for compatibility  with  earlier
       Postfix	behavior.  Prior  to  Postfix 2.5, the default value was 5, but the limit was not
       actually enforced. If you have set this to a lower non-default  value,  certificates  with
       longer trust chains may now fail to verify. Certificate chains with 1 or 2 CAs are common,
       deeper chains are more rare and any number between 5 and 9 should suffice in practice. You
       can  choose  a  lower number if, for example, you trust certificates directly signed by an
       issuing CA but not any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cert_file (default: empty)
       File with the Postfix SMTP server RSA certificate in PEM format.  This file may also  con-
       tain the Postfix SMTP server private RSA key.

       Public  Internet  MX  hosts without certificates signed by a "reputable" CA must generate,
       and be prepared to present to most clients, a self-signed or  private-CA  signed  certifi-
       cate.  The  client  will  not be able to authenticate the server, but unless it is running
       Postfix 2.3 or similar software, it will still insist on a server certificate.

       For servers that are not public Internet MX hosts,  Postfix  2.3  supports  configurations
       with  no  certificates.	This entails the use of just the anonymous TLS ciphers, which are
       not supported by typical SMTP clients. Since such clients will not, as a rule,  fall  back
       to  plain  text	after a TLS handshake failure, the server will be unable to receive email
       from TLS enabled clients. To avoid accidental configurations with no certificates, Postfix
       2.3  enables  certificate-less  operation  only	when  the  administrator  explicitly sets
       "smtpd_tls_cert_file = none". This ensures that new Postfix configurations will not  acci-
       dentally run with no certificates.

       Both RSA and DSA certificates are supported.  When both types are present, the cipher used
       determines which certificate will be presented to the client.  For  Netscape  and  OpenSSL
       clients without special cipher choices the RSA certificate is preferred.

       To  enable a remote SMTP client to verify the Postfix SMTP server certificate, the issuing
       CA certificates must be made available to the client. You should include the required cer-
       tificates  in  the server certificate file, the server certificate first, then the issuing
       CA(s) (bottom-up order).

       Example: the certificate for "server.example.com" was issued by	"intermediate  CA"  which
       itself	has   a  certificate  of  "root  CA".	Create	the  server.pem  file  with  "cat
       server_cert.pem intermediate_CA.pem root_CA.pem > server.pem".

       If you also want to verify client certificates issued by these CAs, you	can  add  the  CA
       certificates  to  the  smtpd_tls_CAfile, in which case it is not necessary to have them in
       the smtpd_tls_cert_file or smtpd_tls_dcert_file.

       A certificate supplied here must be usable as an SSL server certificate and hence pass the
       "openssl verify -purpose sslserver ..." test.

       Example:

       smtpd_tls_cert_file = /etc/postfix/server.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cipherlist (default: empty)
       Obsolete  Postfix < 2.3 control for the Postfix SMTP server TLS cipher list. It is easy to
       create inter-operability problems by choosing a non-default cipher list. Do not use a non-
       default	TLS  cipherlist  for  MX hosts on the public Internet. Clients that begin the TLS
       handshake, but are unable to agree on a common cipher, may not be able to send  any  email
       to the SMTP server. Using a restricted cipher list may be more appropriate for a dedicated
       MSA or an internal mailhub, where one can exert some control over  the  TLS  software  and
       settings of the connecting clients.

       Note: do not use "" quotes around the parameter value.

       This  feature  is  available with Postfix version 2.2. It is not used with Postfix 2.3 and
       later; use smtpd_tls_mandatory_ciphers instead.

smtpd_tls_ciphers (default: export)
       The minimum TLS cipher grade that the Postfix SMTP server will use with opportunistic  TLS
       encryption.  Cipher  types  listed in smtpd_tls_exclude_ciphers are excluded from the base
       definition of the selected cipher grade. The default value "export" ensures maximum inter-
       operability.  Because  encryption  is optional, stronger controls are not appropriate, and
       this setting SHOULD NOT be changed unless the change is essential.

       When TLS is mandatory the cipher grade is chosen via the smtpd_tls_mandatory_ciphers  con-
       figuration parameter, see there for syntax details.

       Example:
       smtpd_tls_ciphers = export

       This feature is available in Postfix 2.6 and later. With earlier Postfix releases only the
       smtpd_tls_mandatory_ciphers parameter is implemented, and opportunistic	TLS  always  uses
       "export" or better (i.e. all) ciphers.

smtpd_tls_dcert_file (default: empty)
       File  with the Postfix SMTP server DSA certificate in PEM format.  This file may also con-
       tain the Postfix SMTP server private DSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_dcert_file = /etc/postfix/server-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_dh1024_param_file (default: empty)
       File with DH parameters that the Postfix SMTP server should use with EDH ciphers.

       Instead of using the exact same parameter sets as distributed with other TLS packages,  it
       is  more  secure  to generate your own set of parameters with something like the following
       command:

	   openssl gendh -out /etc/postfix/dh_1024.pem -2 1024

       Your actual source for entropy may differ. Some systems have /dev/random; on other  system
       you may consider using the "Entropy Gathering Daemon EGD", available at http://egd.source-
       forge.net/

       Example:

       smtpd_tls_dh1024_param_file = /etc/postfix/dh_1024.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dh512_param_file (default: empty)
       File with DH parameters that the Postfix SMTP server should use with EDH ciphers.

       See also the discussion under the smtpd_tls_dh1024_param_file configuration parameter.

       Example:

       smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file)
       File with the Postfix SMTP server DSA private key in PEM format.  This file  may  be  com-
       bined   with   the   Postfix   SMTP   server   DSA   certificate   file	 specified   with
       $smtpd_tls_dcert_file.

       The private key must be accessible without a pass-phrase, i.e. it must not  be  encrypted.
       File  permissions  should grant read-only access to the system superuser account ("root"),
       and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_eccert_file (default: empty)
       File with the Postfix SMTP server ECDSA certificate in PEM format.   This  file	may  also
       contain the Postfix SMTP server private ECDSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_eccert_file = /etc/postfix/ecdsa-scert.pem

       This  feature  is  available in Postfix 2.6 and later, when Postfix is compiled and linked
       with OpenSSL 1.0.0 or later.

smtpd_tls_eckey_file (default: $smtpd_tls_eccert_file)
       File with the Postfix SMTP server ECDSA private key in PEM format.  This file may be  com-
       bined   with   the   Postfix   SMTP   server   ECDSA   certificate   file  specified  with
       $smtpd_tls_eccert_file.

       The private key must be accessible without a pass-phrase, i.e. it must not  be  encrypted.
       File  permissions  should grant read-only access to the system superuser account ("root"),
       and no access to anyone else.

       This feature is available in Postfix 2.6 and later, when Postfix is  compiled  and  linked
       with OpenSSL 1.0.0 or later.

smtpd_tls_eecdh_grade (default: see postconf -d output)
       The Postfix SMTP server security grade for ephemeral elliptic-curve Diffie-Hellman (EECDH)
       key exchange.

       The available choices are:

       none   Don't use EECDH. Ciphers based on EECDH key exchange will be disabled. This is  the
	      default in Postfix versions 2.6 and 2.7.

       strong Use  EECDH  with	approximately  128 bits of security at a reasonable computational
	      cost. This is the current best-practice trade-off  between  security  and  computa-
	      tional efficiency. This is the default in Postfix version 2.8 and later.

       ultra  Use  EECDH  with	approximately  192 bits of security at computational cost that is
	      approximately twice as high as 128 bit strength ECC. Barring  significant  progress
	      in  attacks  on elliptic curve crypto-systems, the "strong" curve is sufficient for
	      most users.

       This feature is available in Postfix 2.6 and later, when it is compiled	and  linked  with
       OpenSSL 1.0.0 or later.

smtpd_tls_exclude_ciphers (default: empty)
       List  of  ciphers  or  cipher types to exclude from the SMTP server cipher list at all TLS
       security levels. Excluding valid ciphers can  create  interoperability  problems.  DO  NOT
       exclude	ciphers unless it is essential to do so. This is not an OpenSSL cipherlist; it is
       a simple list separated by whitespace and/or commas. The elements are a single cipher,  or
       one  or	more "+" separated cipher properties, in which case only ciphers matching all the
       properties are excluded.

       Examples (some of these will cause problems):

	   smtpd_tls_exclude_ciphers = aNULL
	   smtpd_tls_exclude_ciphers = MD5, DES
	   smtpd_tls_exclude_ciphers = DES+MD5
	   smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
	   smtpd_tls_exclude_ciphers = kEDH+aRSA

       The first setting disables anonymous ciphers. The next setting disables ciphers	that  use
       the  MD5  digest algorithm or the (single) DES encryption algorithm. The next setting dis-
       ables ciphers that use MD5 and DES together.  The next setting disables	the  two  ciphers
       "AES256-SHA"  and  "DES-CBC3-MD5".  The	last  setting disables ciphers that use "EDH" key
       exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_fingerprint_digest (default: md5)
       The message digest algorithm to construct remote SMTP client-certificate  fingerprints  or
       public	key  fingerprints  (Postfix  2.9  and  later)  for  check_ccert_access	and  per-
       mit_tls_clientcerts. The default algorithm is md5, for backwards compatibility with  Post-
       fix releases prior to 2.5.

       Advances in hash function cryptanalysis have led to md5 being deprecated in favor of sha1.
       However, as long as there are no known "second pre-image" attacks against md5, its use  in
       this context can still be considered safe.

       While  additional  digest  algorithms  are  often available with OpenSSL's libcrypto, only
       those used by libssl in SSL cipher suites are available to Postfix.

       To find the fingerprint of a specific certificate file, with a specific digest  algorithm,
       run:

	   $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The text to the right of "=" sign is the desired fingerprint.  For example:

	   $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
	   SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       To  extract  the public key fingerprint from an X.509 certificate, you need to extract the
       public key from the certificate and compute the appropriate  digest  of	its  DER  (ASN.1)
       encoding.  With OpenSSL the "-pubkey" option of the "x509" command extracts the public key
       always in "PEM" format. We pipe the result to another OpenSSL command  that  converts  the
       key to DER and then to the "dgst" command to compute the fingerprint.

       The  actual  command  to transform the key to DER format depends on the version of OpenSSL
       used. With OpenSSL 1.0.0 and later, the	"pkey"	command  supports  all	key  types.  With
       OpenSSL	0.9.8  and  earlier, the key type is always RSA (nobody uses DSA, and EC keys are
       not fully supported by 0.9.8), so the "rsa" command is used.

	   # OpenSSL 1.0 with all certificates and SHA-1 fingerprints.
	   $ openssl x509 -in cert.pem -noout -pubkey |
	       openssl pkey -pubin -outform DER |
	       openssl dgst -sha1 -c
	   (stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58

	   # OpenSSL 0.9.8 with RSA certificates and MD5 fingerprints.
	   $ openssl x509 -in cert.pem -noout -pubkey |
	       openssl rsa -pubin -outform DER |
	       openssl dgst -md5 -c
	   (stdin)= f4:62:60:f6:12:8f:d5:8d:28:4d:13:a7:db:b2:ff:50

       The Postfix SMTP server and client log the peer (leaf) certificate fingerprint and  public
       key fingerprint when the TLS loglevel is 2 or higher.

       Note:  Postfix  2.9.0&ndash;2.9.5  computed the public key fingerprint incorrectly. To use
       public-key fingerprints, upgrade to Postfix 2.9.6 or later.

       Example: client-certificate access table, with sha1 fingerprints:

	   /etc/postfix/main.cf:
	       smtpd_tls_fingerprint_digest = sha1
	       smtpd_client_restrictions =
		   check_ccert_access hash:/etc/postfix/access,
		   reject
	   /etc/postfix/access:
	       # Action folded to next line...
	       AF:88:7C:AD:51:95:6F:36:96:F6:01:FB:2E:48:CD:AB:49:25:A2:3B
		   OK
	       85:16:78:FD:73:6E:CE:70:E0:31:5F:0D:3C:C8:6D:C4:2C:24:59:E1
		   permit_auth_destination

       This feature is available in Postfix 2.5 and later.

smtpd_tls_key_file (default: $smtpd_tls_cert_file)
       File with the Postfix SMTP server RSA private key in PEM format.  This file  may  be  com-
       bined   with   the   Postfix   SMTP   server   RSA   certificate   file	 specified   with
       $smtpd_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it must not  be  encrypted.
       File  permissions  should grant read-only access to the system superuser account ("root"),
       and no access to anyone else.

smtpd_tls_loglevel (default: 0)
       Enable additional Postfix SMTP server logging of TLS activity.  Each  logging  level  also
       includes the information that is logged at a lower logging level.

	      0  Log  only  a  summary	message on TLS handshake completion &mdash; no logging of
	      remote SMTP client certificate trust-chain verification errors if  client  certifi-
	      cate verification is not required. With Postfix 2.8 and earlier, disable logging of
	      TLS activity.

	      1 Also log trust-chain verification errors and peer certificate  name  and  issuer.
	      With Postfix 2.8 and earlier, log TLS handshake and certificate information.

	      2 Also log levels during TLS negotiation.

	      3 Also log hexadecimal and ASCII dump of TLS negotiation process.

	      4 Also log hexadecimal and ASCII dump of complete transmission after STARTTLS.

       Do  not use "smtpd_tls_loglevel = 2" or higher except in case of problems. Use of loglevel
       4 is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP server  will	use  with  mandatory  TLS
       encryption.  The  default  grade  ("medium")  is sufficiently strong that any benefit from
       globally restricting TLS sessions to a more stringent grade is  likely  negligible,  espe-
       cially  given  the  fact that many implementations still do not offer any stronger ("high"
       grade) ciphers, while those that do, will always use "high" grade ciphers. So insisting on
       "high"  grade  ciphers is generally counter-productive. Allowing "export" or "low" ciphers
       is typically not a good idea, as systems limited to just these  are  limited  to  obsolete
       browsers.  No  known  SMTP  clients  fail to support at least one "medium" or "high" grade
       cipher.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or stronger OpenSSL ciphers.  This is  the	most  appropriate
	      setting  for public MX hosts, and is always used with opportunistic TLS encryption.
	      The underlying cipherlist is specified via the tls_export_cipherlist  configuration
	      parameter, which you are strongly encouraged to not change.

       low    Enable "LOW" grade or stronger OpenSSL ciphers. The underlying cipherlist is speci-
	      fied via the tls_low_cipherlist configuration parameter,	which  you  are  strongly
	      encouraged to not change.

       medium Enable "MEDIUM" grade or stronger OpenSSL ciphers. These use 128-bit or longer sym-
	      metric bulk-encryption keys. This is the default minimum strength for mandatory TLS
	      encryption.  The	underlying  cipherlist is specified via the tls_medium_cipherlist
	      configuration parameter, which you are strongly encouraged to not change.

       high   Enable only "HIGH" grade OpenSSL ciphers. The underlying	cipherlist  is	specified
	      via the tls_high_cipherlist configuration parameter, which you are strongly encour-
	      aged to not change.

       null   Enable only the  "NULL"  OpenSSL	ciphers,  these  provide  authentication  without
	      encryption.  This setting is only appropriate in the rare case that all clients are
	      prepared to use NULL ciphers (not normally enabled in TLS clients). The  underlying
	      cipherlist  is specified via the tls_null_cipherlist configuration parameter, which
	      you are strongly encouraged to not change.

       Cipher types listed in  smtpd_tls_mandatory_exclude_ciphers  or	smtpd_tls_exclude_ciphers
       are  excluded from the base definition of the selected cipher grade. See smtpd_tls_ciphers
       for cipher controls that apply to opportunistic TLS.

       The underlying cipherlists for grades other than "null"	include  anonymous  ciphers,  but
       these  are  automatically  filtered out if the server is configured to ask for remote SMTP
       client certificates.  You are very unlikely to need to take any steps to exclude anonymous
       ciphers,  they  are  excluded  automatically  as  required.  If you must exclude anonymous
       ciphers	even   when   Postfix	does   not   need   or	 use   peer   certificates,   set
       "smtpd_tls_exclude_ciphers  =  aNULL".  To  exclude  anonymous  ciphers	only  when TLS is
       enforced, set "smtpd_tls_mandatory_exclude_ciphers = aNULL".

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_exclude_ciphers (default: empty)
       Additional list of ciphers or cipher types to exclude from the Postfix SMTP server  cipher
       list  at  mandatory  TLS  security  levels.  This list works in addition to the exclusions
       listed with smtpd_tls_exclude_ciphers (see there for syntax details).

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_protocols (default: !SSLv2)
       The SSL/TLS protocols accepted by the Postfix SMTP server with mandatory  TLS  encryption.
       If the list is empty, the server supports all available SSL/TLS protocol versions.  A non-
       empty value is a list of protocol names separated by whitespace,  commas  or  colons.  The
       supported protocol names are "SSLv2", "SSLv3" and "TLSv1", and are not case sensitive.

       Note:  As  of  OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and "TLSv1.2". If an
       older Postfix version is linked against OpenSSL 1.0.1 or later, these, or  any  other  new
       protocol versions, are unconditionally enabled.

       With  Postfix  >= 2.5 the parameter syntax is expanded to support protocol exclusions. One
       can now explicitly exclude SSLv2 by setting "smtpd_tls_mandatory_protocols =  !SSLv2".  To
       exclude both SSLv2 and SSLv3 set "smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing
       the protocols to include, rather than protocols to exclude, is supported, but  not  recom-
       mended.	The  exclusion form more closely matches the behavior when the OpenSSL library is
       newer than Postfix.

       Since SSL version 2 has known protocol weaknesses and is now deprecated, the default  set-
       ting  excludes "SSLv2".	This means that by default, SSL version 2 will not be used at the
       "encrypt" security level.

       Example:

       smtpd_tls_mandatory_protocols = TLSv1
       # Alternative form with Postfix >= 2.5:
       smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.3 and later.

smtpd_tls_protocols (default: empty)
       List of TLS protocols that the Postfix SMTP server will exclude	or  include  with  oppor-
       tunistic  TLS encryption. This parameter SHOULD be left at its default empty value, allow-
       ing all protocols to be used with opportunistic TLS.

       In main.cf the values are separated by whitespace, commas or colons. An empty value  means
       allow all protocols. The valid protocol names, (see \fBfBSSL_get_version(3)), are "SSLv2",
       "SSLv3" and "TLSv1". In smtp_tls_policy_maps table entries, "protocols"	attribute  values
       are separated by a colon.

       Note:  As  of  OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and "TLSv1.2". If an
       older Postfix version is linked against OpenSSL 1.0.1 or later, these, or  any  other  new
       protocol versions, are unconditionally enabled.

       To  include a protocol list its name, to exclude it, prefix the name with a "!" character.
       To exclude SSLv2 even for opportunistic TLS set "smtpd_tls_protocols = !SSLv2". To exclude
       both  "SSLv2"  and  "SSLv3" set "smtpd_tls_protocols = !SSLv2, !SSLv3". Explicitly listing
       the protocols to include, rather than protocols to exclude, is supported, but  not  recom-
       mended.	 The exclusion form more closely matches the behavior when the OpenSSL library is
       newer than Postfix.

       Example:
       smtpd_tls_protocols = !SSLv2

       This feature is available in Postfix 2.6 and later.

smtpd_tls_received_header (default: no)
       Request that the Postfix SMTP server produces  Received:   message  headers  that  include
       information  about the protocol and cipher used, as well as the remote SMTP client Common-
       Name and client certificate issuer CommonName.  This is disabled by default, as the infor-
       mation  may  be modified in transit through other mail servers.	Only information that was
       recorded by the final destination can be trusted.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_req_ccert (default: no)
       With mandatory TLS encryption, require a trusted remote SMTP client certificate	in  order
       to allow TLS connections to proceed.  This option implies "smtpd_tls_ask_ccert = yes".

       When  TLS  encryption  is  optional, this setting is ignored with a warning written to the
       mail log.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_security_level (default: empty)
       The SMTP TLS security level for the Postfix SMTP server; when a non-empty value is  speci-
       fied,  this  overrides  the  obsolete parameters smtpd_use_tls and smtpd_enforce_tls. This
       parameter is ignored with "smtpd_tls_wrappermode = yes".

       Specify one of the following security levels:

       none   TLS will not be used.

       may    Opportunistic TLS: announce STARTTLS support to remote SMTP  clients,  but  do  not
	      require that clients use TLS encryption.

       encrypt
	      Mandatory  TLS  encryption:  announce  STARTTLS support to remote SMTP clients, and
	      require that clients use TLS encryption. According to RFC 2487  this  MUST  NOT  be
	      applied  in  case of a publicly-referenced SMTP server. Instead, this option should
	      be used only on dedicated servers.

       Note 1: the "fingerprint", "verify" and "secure" levels are not supported here.	The Post-
       fix  SMTP  server logs a warning and uses "encrypt" instead.  To verify remote SMTP client
       certificates,   see   TLS_README   for	a   discussion	 of   the    smtpd_tls_ask_ccert,
       smtpd_tls_req_ccert, and permit_tls_clientcerts features.

       Note   2:   The	 parameter   setting   "smtpd_tls_security_level   =   encrypt"   implies
       "smtpd_tls_auth_only = yes".

       Note 3: when invoked via "sendmail -bs", Postfix will never offer STARTTLS due to insuffi-
       cient privileges to access the server private key. This is intended behavior.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_session_cache_database (default: empty)
       Name  of the file containing the optional Postfix SMTP server TLS session cache. Specify a
       database type that supports enumeration, such as btree or sdbm; there is no need  to  sup-
       port  concurrent  access.   The	file is created if it does not exist. The smtpd(8) daemon
       does not use this parameter directly, rather the cache is implemented  indirectly  in  the
       tlsmgr(8) daemon. This means that per-smtpd-instance master.cf overrides of this parameter
       are not effective. Note, that each of the cache databases supported by  tlsmgr(8)  daemon:
       $smtpd_tls_session_cache_database,  $smtp_tls_session_cache_database (and with Postfix 2.3
       and later $lmtp_tls_session_cache_database), needs to be stored separately. It is  not  at
       this time possible to store multiple caches in a single database.

       Note: dbm databases are not suitable. TLS session objects are too large.

       As of version 2.5, Postfix no longer uses root privileges when opening this file. The file
       should now be stored under the  Postfix-owned  data_directory.  As  a  migration  aid,  an
       attempt	to open the file under a non-Postfix directory is redirected to the Postfix-owned
       data_directory, and a warning is logged.

       Example:

       smtpd_tls_session_cache_database = btree:/var/lib/postfix/smtpd_scache

       This feature is available in Postfix 2.2 and later.

smtpd_tls_session_cache_timeout (default: 3600s)
       The expiration time of Postfix SMTP server TLS session cache information. A cache  cleanup
       is   performed	periodically  every  $smtpd_tls_session_cache_timeout  seconds.  As  with
       $smtpd_tls_session_cache_database, this parameter is implemented in the	tlsmgr(8)  daemon
       and therefore per-smtpd-instance master.cf overrides are not possible.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_wrappermode (default: no)
       Run  the  Postfix  SMTP	server	in  the non-standard "wrapper" mode, instead of using the
       STARTTLS command.

       If you want to support this service, enable a special port in master.cf, and  specify  "-o
       smtpd_tls_wrappermode=yes"  on  the  SMTP server's command line. Port 465 (smtps) was once
       chosen for this purpose.

       This feature is available in Postfix 2.2 and later.

smtpd_upstream_proxy_protocol (default: empty)
       The name of the proxy protocol used by an optional before-smtpd proxy agent. When a  proxy
       agent is used, this protocol conveys local and remote address and port information.  Spec-
       ify "smtpd_upstream_proxy_protocol = haproxy" to enable the haproxy protocol.

       NOTE: To use the nginx proxy with smtpd(8), enable the XCLIENT protocol with  smtpd_autho-
       rized_xclient_hosts. This supports SASL authentication in the proxy agent (Postfix 2.9 and
       later).

       This feature is available in Postfix 2.10 and later.

smtpd_upstream_proxy_timeout (default: 5s)
       The time limit for the proxy protocol  specified  with  the  smtpd_upstream_proxy_protocol
       parameter.

       This feature is available in Postfix 2.10 and later.

smtpd_use_tls (default: no)
       Opportunistic  TLS:  announce  STARTTLS support to remote SMTP clients, but do not require
       that clients use TLS encryption.

       Note: when invoked via "sendmail -bs", Postfix will never offer STARTTLS due  to  insuffi-
       cient privileges to access the server private key. This is intended behavior.

       This  feature  is  available  in  Postfix  2.2  and  later. With Postfix 2.3 and later use
       smtpd_tls_security_level instead.

soft_bounce (default: no)
       Safety net to keep mail queued that would otherwise  be	returned  to  the  sender.   This
       parameter  disables  locally-generated bounces, changes the handling of negative responses
       from remote servers, content filters or plugins, and prevents the Postfix SMTP server from
       rejecting  mail permanently by changing 5xx reply codes into 4xx.  However, soft_bounce is
       no cure for address rewriting mistakes or mail routing mistakes.

       Note: "soft_bounce = yes" is in some cases  implemented	by  modifying  server  responses.
       Therefore,  the response that Postfix logs may differ from the response that Postfix actu-
       ally sends or receives.

       Example:

       soft_bounce = yes

stale_lock_time (default: 500s)
       The time after which a stale exclusive mailbox lockfile is  removed.   This  is	used  for
       delivery to file or mailbox.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

stress (default: empty)
       This feature is documented in the STRESS_README document.

       This feature is available in Postfix 2.5 and later.

strict_7bit_headers (default: no)
       Reject mail with 8-bit text in message headers.	This  blocks  mail  from  poorly  written
       applications.

       This  feature should not be enabled on a general purpose mail server, because it is likely
       to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime (default: no)
       Enable both strict_7bit_headers and strict_8bitmime_body.

       This feature should not be enabled on a general purpose mail server, because it is  likely
       to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime_body (default: no)
       Reject  8-bit  message  body  text  without 8-bit MIME content encoding information.  This
       blocks mail from poorly written applications.

       Unfortunately, this also rejects majordomo approval requests  when  the	included  request
       contains  valid	8-bit  MIME  mail,  and  it rejects bounces from mailers that do not MIME
       encapsulate 8-bit content (for example, bounces from qmail or from old versions	of  Post-
       fix).

       This  feature should not be enabled on a general purpose mail server, because it is likely
       to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_mailbox_ownership (default: yes)
       Defer delivery when a mailbox file is not owned by its recipient.  The default setting  is
       not backwards compatible.

       This feature is available in Postfix 2.5.3 and later.

strict_mime_encoding_domain (default: no)
       Reject  mail with invalid Content-Transfer-Encoding: information for the message/* or mul-
       tipart/* MIME content types.  This blocks mail from poorly written software.

       This feature should not be enabled on a general	purpose  mail  server,	because  it  will
       reject mail after a single violation.

       This feature is available in Postfix 2.0 and later.

strict_rfc821_envelopes (default: no)
       Require	that  addresses received in SMTP MAIL FROM and RCPT TO commands are enclosed with
       <>, and that those addresses do not contain RFC 822 style comments or phrases.  This stops
       mail from poorly written software.

       By  default,  the  Postfix  SMTP  server  accepts  RFC 822 syntax in MAIL FROM and RCPT TO
       addresses.

sun_mailtool_compatibility (default: no)
       Obsolete SUN mailtool compatibility feature. Instead, use  "mailbox_delivery_lock  =  dot-
       lock".

swap_bangpath (default: yes)
       Enable  the  rewriting of "site!user" into "user@site".	This is necessary if your machine
       is connected to UUCP networks.  It is enabled by default.

       Note: with Postfix version 2.2, message header address rewriting happens only when one  of
       the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The  message  is	received  from	a  network  client that matches $local_header_re-
	      write_clients,

       o      The message is received from  the  network,  and	the  remote_header_rewrite_domain
	      parameter specifies a non-empty value.

       To  get	the  behavior before Postfix version 2.2, specify "local_header_rewrite_clients =
       static:all".

       Example:

       swap_bangpath = no

syslog_facility (default: mail)
       The syslog facility of Postfix logging. Specify a facility as defined  in  syslog.conf(5).
       The default facility is "mail".

       Warning:  a  non-default syslog_facility setting takes effect only after a Postfix process
       has completed initialization.  Errors during process initialization will  be  logged  with
       the  default  facility.	Examples are errors while parsing the command line arguments, and
       errors while accessing the Postfix main.cf configuration file.

syslog_name (default: see postconf -d output)
       The mail system name that is prepended to the process name  in  syslog  records,  so  that
       "smtpd" becomes, for example, "postfix/smtpd".

       Warning:  a  non-default syslog_name setting takes effect only after a Postfix process has
       completed initialization. Errors during process initialization will  be	logged	with  the
       default	name.  Examples  are  errors while parsing the command line arguments, and errors
       while accessing the Postfix main.cf configuration file.

tcp_windowsize (default: 0)
       An optional workaround for routers that break TCP window scaling.  Specify a value > 0 and
       <  65536 to enable this feature.  With Postfix TCP servers (smtpd(8), qmqpd(8)), this fea-
       ture is implemented by the Postfix master(8) daemon.

       To change this parameter without stopping Postfix, you need to first terminate all Postfix
       TCP servers:

	   # postconf -e master_service_disable=inet
	   # postfix reload

       This  immediately  terminates  all  processes  that accept network connections.	Next, you
       enable Postfix TCP servers with the updated tcp_windowsize setting:

	   # postconf -e tcp_windowsize=65535 master_service_disable=
	   # postfix reload

       If you skip these steps with a running Postfix system, then the tcp_windowsize change will
       work only for Postfix TCP clients (smtp(8), lmtp(8)).

       This feature is available in Postfix 2.6 and later.

tls_append_default_CA (default: no)
       Append  the  system-supplied default certificate authority certificates to the ones speci-
       fied with *_tls_CApath or *_tls_CAfile.	The default is "no"; this prevents  Postfix  from
       trusting   third-party	certificates   and   giving   them  relay  permission  with  per-
       mit_tls_all_clientcerts.

       This feature is available in Postfix 2.4.15, 2.5.11,  2.6.8,  2.7.2  and  later	versions.
       Specify	"tls_append_default_CA = yes" for backwards compatibility, to avoid breaking cer-
       tificate verification with sites that don't use permit_tls_all_clientcerts.

tls_daemon_random_bytes (default: 32)
       The number of pseudo-random bytes that an smtp(8) or smtpd(8) process  requests	from  the
       tlsmgr(8) server in order to seed its internal pseudo random number generator (PRNG).  The
       default of 32 bytes (equivalent to 256 bits)  is  sufficient  to  generate  a  128bit  (or
       168bit) session key.

       This feature is available in Postfix 2.2 and later.

tls_disable_workarounds (default: see postconf -d output)
       List or bit-mask of OpenSSL bug work-arounds to disable.

       The  OpenSSL  toolkit  includes	a  set of work-arounds for buggy SSL/TLS implementations.
       Applications, such as Postfix, that want to  maximize  interoperability	ask  the  OpenSSL
       library to enable the full set of recommended work-arounds.

       From  time  to  time,  it  is  discovered that a work-around creates a security issue, and
       should no longer be used. If upgrading OpenSSL to a fixed version is not an option  or  an
       upgrade	is  not  available  in	a timely manner, or in closed environments where no buggy
       clients or servers exist, it may be appropriate to disable some	or  all  of  the  OpenSSL
       interoperability work-arounds. This parameter specifies which bug work-arounds to disable.

       If  the	value  of the parameter is a hexadecimal long integer starting with "0x", the bug
       work-arounds corresponding to the bits  specified  in  its  value  are  removed	from  the
       SSL_OP_ALL  work-around	bit-mask  (see openssl/ssl.h and SSL_CTX_set_options(3)). You can
       specify more bits than are present in SSL_OP_ALL,  excess  bits	are  ignored.  Specifying
       0xFFFFFFFF disables all bug-workarounds on a 32-bit system. This should also be sufficient
       on 64-bit systems, until OpenSSL abandons support for 32-bit systems and starts using  the
       high 32 bits of a 64-bit bug-workaround mask.

       Otherwise,  the	parameter  is a white-space or comma separated list of specific named bug
       work-arounds chosen from the list below. It is possible that your OpenSSL version includes
       new  bug  work-arounds added after your Postfix source code was last updated, in that case
       you can only disable one of these via the hexadecimal syntax above.

       MICROSOFT_SESS_ID_BUG
	      See SSL_CTX_set_options(3)

       NETSCAPE_CHALLENGE_BUG
	      See SSL_CTX_set_options(3)

       LEGACY_SERVER_CONNECT
	      See SSL_CTX_set_options(3)

       NETSCAPE_REUSE_CIPHER_CHANGE_BUG
	      also aliased as CVE-2010-4180. Postfix 2.8 disables  this  work-around  by  default
	      with OpenSSL versions that may predate the fix. Fixed in OpenSSL 0.9.8q and OpenSSL
	      1.0.0c.

       SSLREF2_REUSE_CERT_TYPE_BUG
	      See SSL_CTX_set_options(3)

       MICROSOFT_BIG_SSLV3_BUFFER
	      See SSL_CTX_set_options(3)

       MSIE_SSLV2_RSA_PADDING
	      also aliased as CVE-2005-2969. Postfix 2.8 disables  this  work-around  by  default
	      with OpenSSL versions that may predate the fix. Fixed in OpenSSL 0.9.7h and OpenSSL
	      0.9.8a.

       SSLEAY_080_CLIENT_DH_BUG
	      See SSL_CTX_set_options(3)

       TLS_D5_BUG
	      See SSL_CTX_set_options(3)

       TLS_BLOCK_PADDING_BUG
	      See SSL_CTX_set_options(3)

       TLS_ROLLBACK_BUG
	      See SSL_CTX_set_options(3).  This is disabled in OpenSSL 0.9.7  and  later.  Nobody
	      should still be using 0.9.6!

       DONT_INSERT_EMPTY_FRAGMENTS
	      See SSL_CTX_set_options(3)

       CRYPTOPRO_TLSEXT_BUG
	      New with GOST support in OpenSSL 1.0.0.

       This feature is available in Postfix 2.8 and later.

tls_eecdh_strong_curve (default: prime256v1)
       The  elliptic curve used by the Postfix SMTP server for sensibly strong ephemeral ECDH key
       exchange. This curve is used by the Postfix  SMTP  server  when	"smtpd_tls_eecdh_grade	=
       strong".  The  phrase "sensibly strong" means approximately 128-bit security based on best
       known attacks. The  selected  curve  must  be  implemented  by  OpenSSL	(as  reported  by
       ecparam(1)  with  the  "-list_curves"  option)  and be one of the curves listed in Section
       5.1.1 of RFC 4492. You should not generally change this setting.

       This   default	curve	is   specified	 in   NSA    "Suite    B"    Cryptography    (see
       http://www.nsa.gov/ia/industry/crypto_suite_b.cfm) for information classified as SECRET.

       Note: elliptic curve names are poorly standardized; different standards groups are assign-
       ing different names to the  same  underlying  curves.   The  curve  with  the  X9.62  name
       "prime256v1" is also known under the SECG name "secp256r1", but OpenSSL does not recognize
       the latter name.

       This feature is available in Postfix 2.6 and later, when it is compiled	and  linked  with
       OpenSSL 1.0.0 or later.

tls_eecdh_ultra_curve (default: secp384r1)
       The elliptic curve used by the Postfix SMTP server for maximally strong ephemeral ECDH key
       exchange. This curve is used by the Postfix  SMTP  server  when	"smtpd_tls_eecdh_grade	=
       ultra".	The  phrase "maximally strong" means approximately 192-bit security based on best
       known attacks.  This additional strength comes at a significant computational  cost,  most
       users  should  instead  set  "smtpd_tls_eecdh_grade = strong".  The selected curve must be
       implemented by OpenSSL (as reported by ecparam(1) with the "-list_curves" option)  and  be
       one  of	the  curves  listed in Section 5.1.1 of RFC 4492. You should not generally change
       this setting.

       This  default  "ultra"  curve  is  specified  in   NSA	"Suite	 B"   Cryptography   (see
       http://www.nsa.gov/ia/industry/crypto_suite_b.cfm)   for  information  classified  as  TOP
       SECRET.

       This feature is available in Postfix 2.6 and later, when it is compiled	and  linked  with
       OpenSSL 1.0.0 or later.

tls_export_cipherlist (default: ALL:+RC4:@STRENGTH)
       The  OpenSSL  cipherlist for "EXPORT" or higher grade ciphers. This defines the meaning of
       the  "export"  setting  in  smtpd_tls_mandatory_ciphers,  smtp_tls_mandatory_ciphers   and
       lmtp_tls_mandatory_ciphers.  This  is  the  cipherlist  for  the opportunistic ("may") TLS
       client security level and is the default cipherlist for the SMTP server. You are  strongly
       encouraged  to  not  change  this setting. With OpenSSL 1.0.0 and later the cipherlist may
       start with an "aNULL:" prefix, which restores the 0.9.8-compatible ordering of  the  aNULL
       ciphers	to the top of the list when they are enabled. This prefix is not needed with pre-
       vious OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_high_cipherlist (default: ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
       The OpenSSL cipherlist for "HIGH" grade ciphers. This defines the meaning  of  the  "high"
       setting	in  smtpd_tls_mandatory_ciphers,  smtp_tls_mandatory_ciphers  and lmtp_tls_manda-
       tory_ciphers. You are strongly encouraged to not change this setting. With  OpenSSL  1.0.0
       and  later the cipherlist may start with an "aNULL:" prefix, which restores the 0.9.8-com-
       patible ordering of the aNULL ciphers to the top of the list when they are  enabled.  This
       prefix is not needed with previous OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_legacy_public_key_fingerprints (default: no)
       A  temporary  migration	aid  for  sites that use certificate public-key fingerprints with
       Postfix 2.9.0..2.9.5, which use an incorrect algorithm. This parameter has  no  effect  on
       the certificate fingerprint support that is available since Postfix 2.2.

       Specify	"tls_legacy_public_key_fingerprints  = yes" temporarily, pending a migration from
       configuration files with incorrect  Postfix  2.9.0..2.9.5  certificate  public-key  finger
       prints,	to the correct fingerprints used by Postfix 2.9.6 and later.  To compute the cor-
       rect certificate public-key fingerprints, see TLS_README.

       This feature is available in Postfix 2.9.6 and later.

tls_low_cipherlist (default: ALL:!EXPORT:+RC4:@STRENGTH)
       The OpenSSL cipherlist for "LOW" or higher grade ciphers. This defines the meaning of  the
       "low"	setting    in	 smtpd_tls_mandatory_ciphers,	 smtp_tls_mandatory_ciphers   and
       lmtp_tls_mandatory_ciphers. You are strongly encouraged to not change this setting.   With
       OpenSSL	1.0.0  and later the cipherlist may start with an "aNULL:" prefix, which restores
       the 0.9.8-compatible ordering of the aNULL ciphers to the top of the list  when	they  are
       enabled. This prefix is not needed with previous OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
       The  OpenSSL  cipherlist for "MEDIUM" or higher grade ciphers. This defines the meaning of
       the  "medium"  setting  in  smtpd_tls_mandatory_ciphers,  smtp_tls_mandatory_ciphers   and
       lmtp_tls_mandatory_ciphers. This is the default cipherlist for mandatory TLS encryption in
       the TLS client (with anonymous ciphers disabled when verifying server  certificates).  You
       are  strongly  encouraged  to  not  change this setting.  With OpenSSL 1.0.0 and later the
       cipherlist may start with an "aNULL:" prefix, which restores the 0.9.8-compatible ordering
       of  the	aNULL  ciphers	to  the top of the list when they are enabled. This prefix is not
       needed with previous OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_null_cipherlist (default: eNULL:!aNULL)
       The OpenSSL cipherlist for  "NULL"  grade  ciphers  that  provide  authentication  without
       encryption. This defines the meaning of the "null" setting in smtpd_mandatory_tls_ciphers,
       smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers.  You are strongly encouraged to
       not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_preempt_cipherlist (default: no)
       With SSLv3 and later, use the Postfix SMTP server's cipher preference order instead of the
       remote client's cipher preference order.

       By default, the OpenSSL server selects the client's most preferred cipher that the  server
       supports.  With	SSLv3 and later, the server may choose its own most preferred cipher that
       is supported (offered) by the  client.  Setting	"tls_preempt_cipherlist  =  yes"  enables
       server cipher preferences.

       While server cipher selection may in some cases lead to a more secure or performant cipher
       choice, there is some risk of interoperability issues. In the past, some SSL clients  have
       listed lower priority ciphers that they did not implement correctly. If the server chooses
       a cipher that the client prefers less, it may select a cipher whose client  implementation
       is flawed.

       This  feature is available in Postfix 2.8 and later, in combination with OpenSSL 0.9.7 and
       later.

tls_random_bytes (default: 32)
       The number of bytes that tlsmgr(8) reads from $tls_random_source when (re)seeding the  in-
       memory  pseudo  random number generator (PRNG) pool. The default of 32 bytes (256 bits) is
       good enough for 128bit symmetric keys.  If using EGD or a device file, a  maximum  of  255
       bytes is read.

       This feature is available in Postfix 2.2 and later.

tls_random_exchange_name (default: see postconf -d output)
       Name  of  the  pseudo  random  number  generator  (PRNG)  state file that is maintained by
       tlsmgr(8). The file is created when it does not exist, and its length  is  fixed  at  1024
       bytes.

       As  of version 2.5, Postfix no longer uses root privileges when opening this file, and the
       default file location was  changed  from  ${config_directory}/prng_exch	to  ${data_direc-
       tory}/prng_exch.   As  a  migration  aid,  an attempt to open the file under a non-Postfix
       directory is redirected to the Postfix-owned data_directory, and a warning is logged.

       This feature is available in Postfix 2.2 and later.

tls_random_prng_update_period (default: 3600s)
       The time between attempts by tlsmgr(8) to save the state of the pseudo random number  gen-
       erator (PRNG) to the file specified with $tls_random_exchange_name.

       This feature is available in Postfix 2.2 and later.

tls_random_reseed_period (default: 3600s)
       The maximal time between attempts by tlsmgr(8) to re-seed the in-memory pseudo random num-
       ber generator (PRNG) pool from external	sources.   The	actual	time  between  re-seeding
       attempts is calculated using the PRNG, and is between 0 and the time specified.

       This feature is available in Postfix 2.2 and later.

tls_random_source (default: see postconf -d output)
       The  external  entropy  source  for the in-memory tlsmgr(8) pseudo random number generator
       (PRNG) pool. Be sure to specify a non-blocking source.  If this source is  not  a  regular
       file,  the  entropy  source  type must be prepended:  egd:/path/to/egd_socket for a source
       with EGD compatible socket interface, or dev:/path/to/device for a device file.

       Note: on OpenBSD systems specify /dev/arandom when /dev/urandom gives timeout errors.

       This feature is available in Postfix 2.2 and later.

tlsproxy_enforce_tls (default: $smtpd_enforce_tls)
       Mandatory TLS: announce STARTTLS support to remote SMTP clients, and require that  clients
       use TLS encryption. See smtpd_enforce_tls for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_service_name (default: tlsproxy)
       The  name  of  the tlsproxy(8) service entry in master.cf. This service performs plaintext
       <=> TLS ciphertext conversion.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_CAfile (default: $smtpd_tls_CAfile)
       A file containing (PEM format) CA certificates of root CAs trusted to sign  either  remote
       SMTP  client  certificates or intermediate CA certificates.  See smtpd_tls_CAfile for fur-
       ther details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_CApath (default: $smtpd_tls_CApath)
       A directory containing (PEM format) CA certificates of root CAs	trusted  to  sign  either
       remote  SMTP client certificates or intermediate CA certificates. See smtpd_tls_CApath for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_always_issue_session_ids (default: $smtpd_tls_always_issue_session_ids)
       Force the Postfix tlsproxy(8) server to issue a TLS session  id,  even  when  TLS  session
       caching is turned off. See smtpd_tls_always_issue_session_ids for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ask_ccert (default: $smtpd_tls_ask_ccert)
       Ask  a  remote  SMTP  client for a client certificate. See smtpd_tls_ask_ccert for further
       details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ccert_verifydepth (default: $smtpd_tls_ccert_verifydepth)
       The verification depth for remote SMTP client certificates. A depth of 1 is sufficient  if
       the  issuing  CA is listed in a local CA file. See smtpd_tls_ccert_verifydepth for further
       details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_cert_file (default: $smtpd_tls_cert_file)
       File with the Postfix tlsproxy(8) server RSA certificate in PEM	format.   This	file  may
       also  contain the Postfix tlsproxy(8) server private RSA key.  See smtpd_tls_cert_file for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ciphers (default: $smtpd_tls_ciphers)
       The minimum TLS cipher grade that the Postfix tlsproxy(8) server will use with opportunis-
       tic TLS encryption. See smtpd_tls_ciphers for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dcert_file (default: $smtpd_tls_dcert_file)
       File  with  the	Postfix  tlsproxy(8) server DSA certificate in PEM format.  This file may
       also contain the Postfix tlsproxy(8) server private DSA key.  See smtpd_tls_dcert_file for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dh1024_param_file (default: $smtpd_tls_dh1024_param_file)
       File  with  DH parameters that the Postfix tlsproxy(8) server should use with EDH ciphers.
       See smtpd_tls_dh1024_param_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dh512_param_file (default: $smtpd_tls_dh512_param_file)
       File with DH parameters that the Postfix tlsproxy(8) server should use with  EDH  ciphers.
       See smtpd_tls_dh512_param_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dkey_file (default: $smtpd_tls_dkey_file)
       File  with the Postfix tlsproxy(8) server DSA private key in PEM format.  This file may be
       combined  with  the  Postfix  tlsproxy(8)  server  DSA  certificate  file  specified  with
       $smtpd_tls_dcert_file.  See smtpd_tls_dkey_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eccert_file (default: $smtpd_tls_eccert_file)
       File  with  the Postfix tlsproxy(8) server ECDSA certificate in PEM format.  This file may
       also contain the Postfix tlsproxy(8) server private ECDSA key.  See  smtpd_tls_eccert_file
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eckey_file (default: $smtpd_tls_eckey_file)
       File  with  the Postfix tlsproxy(8) server ECDSA private key in PEM format.  This file may
       be combined with the Postfix tlsproxy(8) server	ECDSA  certificate  file  specified  with
       $smtpd_tls_eccert_file.	See smtpd_tls_eckey_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eecdh_grade (default: $smtpd_tls_eecdh_grade)
       The  Postfix tlsproxy(8) server security grade for ephemeral elliptic-curve Diffie-Hellman
       (EECDH) key exchange. See smtpd_tls_eecdh_grade for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_exclude_ciphers (default: $smtpd_tls_exclude_ciphers)
       List of ciphers or cipher types to exclude from the tlsproxy(8) server cipher list at  all
       TLS security levels. See smtpd_tls_exclude_ciphers for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_fingerprint_digest (default: $smtpd_tls_fingerprint_digest)
       The message digest algorithm to construct remote SMTP client-certificate fingerprints. See
       smtpd_tls_fingerprint_digest for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_key_file (default: $smtpd_tls_key_file)
       File with the Postfix tlsproxy(8) server RSA private key in PEM format.	This file may  be
       combined  with  the  Postfix  tlsproxy(8)  server  RSA  certificate  file  specified  with
       $smtpd_tls_cert_file.  See smtpd_tls_key_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_loglevel (default: $smtpd_tls_loglevel)
       Enable additional Postfix tlsproxy(8) server logging of TLS activity.  Each logging  level
       also   includes	 the   information   that  is  logged  at  a  lower  logging  level.  See
       smtpd_tls_loglevel for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_ciphers (default: $smtpd_tls_mandatory_ciphers)
       The minimum TLS cipher grade that the Postfix tlsproxy(8) server will use  with	mandatory
       TLS encryption. See smtpd_tls_mandatory_ciphers for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_exclude_ciphers (default: $smtpd_tls_mandatory_exclude_ciphers)
       Additional  list  of ciphers or cipher types to exclude from the tlsproxy(8) server cipher
       list at mandatory TLS security levels.  See smtpd_tls_mandatory_exclude_ciphers	for  fur-
       ther details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_protocols (default: $smtpd_tls_mandatory_protocols)
       The  SSL/TLS  protocols	accepted  by  the  Postfix  tlsproxy(8) server with mandatory TLS
       encryption. If the list is empty, the server supports all available SSL/TLS protocol  ver-
       sions.  See smtpd_tls_mandatory_protocols for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_protocols (default: $smtpd_tls_protocols)
       List  of  TLS  protocols  that the Postfix tlsproxy(8) server will exclude or include with
       opportunistic TLS encryption. See smtpd_tls_protocols for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_req_ccert (default: $smtpd_tls_req_ccert)
       With mandatory TLS encryption, require a trusted remote SMTP client certificate	in  order
       to allow TLS connections to proceed.  See smtpd_tls_req_ccert for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_security_level (default: $smtpd_tls_security_level)
       The  SMTP TLS security level for the Postfix tlsproxy(8) server; when a non-empty value is
       specified, this overrides the obsolete parameters smtpd_use_tls and smtpd_enforce_tls. See
       smtpd_tls_security_level for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_session_cache_timeout (default: $smtpd_tls_session_cache_timeout)
       The  expiration	time of Postfix tlsproxy(8) server TLS session cache information. A cache
       cleanup is performed  periodically  every  $smtpd_tls_session_cache_timeout  seconds.  See
       smtpd_tls_session_cache_timeout for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_use_tls (default: $smtpd_use_tls)
       Opportunistic  TLS:  announce  STARTTLS support to remote SMTP clients, but do not require
       that clients use TLS encryption. See smtpd_use_tls for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_watchdog_timeout (default: 10s)
       How much time a tlsproxy(8) process may take to process local or remote I/O before  it  is
       terminated  by  a  built-in  watchdog  timer.   This  is  a safety mechanism that prevents
       tlsproxy(8) from becoming non-responsive due to a bug in Postfix itself or in system soft-
       ware.   To  avoid  false  alarms and unnecessary cache corruption this limit cannot be set
       under 10s.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 2.8.

trace_service_name (default: trace)
       The name of the trace service. This service is implemented by  the  bounce(8)  daemon  and
       maintains  a  record  of  mail deliveries and produces a mail delivery report when verbose
       delivery is requested with "sendmail -v".

       This feature is available in Postfix 2.1 and later.

transport_delivery_slot_cost (default: $default_delivery_slot_cost)
       A transport-specific override for the default_delivery_slot_cost  parameter  value,  where
       transport is the master.cf name of the message delivery transport.

       Note:  transport_delivery_slot_cost parameters will not show up in "postconf" command out-
       put before Postfix version 2.9.	This limitation applies to many parameters whose name  is
       a  combination  of  a master.cf service name and a built-in suffix (in this case: "_deliv-
       ery_slot_cost").

transport_delivery_slot_discount (default: $default_delivery_slot_discount)
       A transport-specific override  for  the	default_delivery_slot_discount	parameter  value,
       where transport is the master.cf name of the message delivery transport.

       Note:  transport_delivery_slot_discount	parameters will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is a combination of a master.cf service name and a built-in suffix (in this case: "_deliv-
       ery_slot_discount").

transport_delivery_slot_loan (default: $default_delivery_slot_loan)
       A transport-specific override for the default_delivery_slot_loan  parameter  value,  where
       transport is the master.cf name of the message delivery transport.

       Note:  transport_delivery_slot_loan parameters will not show up in "postconf" command out-
       put before Postfix version 2.9.	This limitation applies to many parameters whose name  is
       a  combination  of  a master.cf service name and a built-in suffix (in this case: "_deliv-
       ery_slot_loan").

transport_destination_concurrency_failed_cohort_limit	(default:    $default_destination_concur-
       rency_failed_cohort_limit)
       A  transport-specific override for the default_destination_concurrency_failed_cohort_limit
       parameter value, where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_failed_cohort_limit parameters will not  show
       up  in  "postconf"  command output before Postfix version 2.9.  This limitation applies to
       many parameters whose name is a combination of a master.cf service  name  and  a  built-in
       suffix (in this case: "_destination_concurrency_failed_cohort_limit").

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_limit (default: $default_destination_concurrency_limit)
       A  transport-specific  override	for  the  default_destination_concurrency_limit parameter
       value, where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_limit parameters will not show up  in  "post-
       conf"  command output before Postfix version 2.9.  This limitation applies to many parame-
       ters whose name is a combination of a master.cf service name and  a  built-in  suffix  (in
       this case: "_destination_concurrency_limit").

transport_destination_concurrency_negative_feedback	(default:    $default_destination_concur-
       rency_negative_feedback)
       A transport-specific override  for  the	default_destination_concurrency_negative_feedback
       parameter value, where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_negative_feedback parameters will not show up
       in "postconf" command output before Postfix version 2.9.  This limitation applies to  many
       parameters  whose  name is a combination of a master.cf service name and a built-in suffix
       (in this case: "_destination_concurrency_negative_feedback").

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_positive_feedback    (default:     $default_destination_concur-
       rency_positive_feedback)
       A  transport-specific  override	for the default_destination_concurrency_positive_feedback
       parameter value, where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_positive_feedback parameters will not show up
       in  "postconf" command output before Postfix version 2.9.  This limitation applies to many
       parameters whose name is a combination of a master.cf service name and a  built-in  suffix
       (in this case: "_destination_concurrency_positive_feedback").

       This feature is available in Postfix 2.5 and later.

transport_destination_rate_delay (default: $default_destination_rate_delay)
       A  transport-specific  override	for  the  default_destination_rate_delay parameter value,
       where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_rate_delay parameters will not show up in "postconf" com-
       mand  output before Postfix version 2.9.  This limitation applies to many parameters whose
       name is a combination of a master.cf service name and a built-in  suffix  (in  this  case:
       "_destination_rate_delay").

       This feature is available in Postfix 2.5 and later.

transport_destination_recipient_limit (default: $default_destination_recipient_limit)
       A transport-specific override for the default_destination_recipient_limit parameter value,
       where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_recipient_limit parameters will not show up in "postconf"
       command	output	before	Postfix  version 2.9.  This limitation applies to many parameters
       whose name is a combination of a master.cf service name and a  built-in	suffix	(in  this
       case: "_destination_recipient_limit").

transport_extra_recipient_limit (default: $default_extra_recipient_limit)
       A transport-specific override for the default_extra_recipient_limit parameter value, where
       transport is the master.cf name of the message delivery transport.

       Note: transport_extra_recipient_limit parameters will not show up  in  "postconf"  command
       output  before Postfix version 2.9.  This limitation applies to many parameters whose name
       is a combination of a master.cf	service  name  and  a  built-in  suffix  (in  this  case:
       "_extra_recipient_limit").

transport_initial_destination_concurrency (default: $initial_destination_concurrency)
       A  transport-specific  override	for  the initial_destination_concurrency parameter value,
       where transport is the master.cf name of the message delivery transport.

       Note: some transport_initial_destination_concurrency parameters will not show up in "post-
       conf"  command output before Postfix version 2.9.  This limitation applies to many parame-
       ters whose name is a combination of a master.cf service name and  a  built-in  suffix  (in
       this case: "_initial_destination_concurrency").

       This feature is available in Postfix 2.5 and later.

transport_maps (default: empty)
       Optional  lookup  tables  with mappings from recipient address to (message delivery trans-
       port, next-hop destination).  See transport(5) for details.

       Specify zero or more "type:table" lookup tables.  If  you  use  this  feature  with  local
       files, run "postmap /etc/postfix/transport" after making a change.

       For safety reasons, as of Postfix 2.3 this feature does not allow $number substitutions in
       regular expression maps.

       Examples:

       transport_maps = dbm:/etc/postfix/transport
       transport_maps = hash:/etc/postfix/transport

transport_minimum_delivery_slots (default: $default_minimum_delivery_slots)
       A transport-specific override  for  the	default_minimum_delivery_slots	parameter  value,
       where transport is the master.cf name of the message delivery transport.

       Note:  transport_minimum_delivery_slots	parameters will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is  a combination of a master.cf service name and a built-in suffix (in this case: "_mini-
       mum_delivery_slots").

transport_recipient_limit (default: $default_recipient_limit)
       A transport-specific override  for  the	default_recipient_limit  parameter  value,  where
       transport is the master.cf name of the message delivery transport.

       Note:  some  transport_recipient_limit  parameters  will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is a combination of a master.cf service name and a built-in suffix (in this case: "_recip-
       ient_limit").

transport_recipient_refill_delay (default: $default_recipient_refill_delay)
       A transport-specific override  for  the	default_recipient_refill_delay	parameter  value,
       where transport is the master.cf name of the message delivery transport.

       Note:  transport_recipient_refill_delay	parameters will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is a combination of a master.cf service name and a built-in suffix (in this case: "_recip-
       ient_refill_delay").

       This feature is available in Postfix 2.4 and later.

transport_recipient_refill_limit (default: $default_recipient_refill_limit)
       A transport-specific override  for  the	default_recipient_refill_limit	parameter  value,
       where transport is the master.cf name of the message delivery transport.

       Note:  transport_recipient_refill_limit	parameters will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is a combination of a master.cf service name and a built-in suffix (in this case: "_recip-
       ient_refill_limit").

       This feature is available in Postfix 2.4 and later.

transport_retry_time (default: 60s)
       The time between attempts by the Postfix queue manager to contact a malfunctioning message
       delivery transport.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

transport_time_limit (default: $command_time_limit)
       A transport-specific override for the command_time_limit parameter value, where	transport
       is the master.cf name of the message delivery transport.

       Note: transport_time_limit parameters will not show up in "postconf" command output before
       Postfix version 2.9.  This limitation applies to many parameters whose name is a  combina-
       tion of a master.cf service name and a built-in suffix (in this case: "_time_limit").

trigger_timeout (default: 10s)
       The  time  limit  for sending a trigger to a Postfix daemon (for example, the pickup(8) or
       qmgr(8) daemon). This time limit prevents programs from getting stuck when the mail system
       is under heavy load.

       Time  units:  s	(seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

undisclosed_recipients_header (default: see postconf -d output)
       Message header that the Postfix cleanup(8) server inserts when a message contains  no  To:
       or  Cc: message header. With Postfix 2.8 and later, the default value is empty. With Post-
       fix 2.4-2.7, specify an empty value to disable this feature.

       Example:

       # Default value before Postfix 2.8.
       # Note: the ":" and ";" are both required.
       undisclosed_recipients_header = To: undisclosed-recipients:;

unknown_address_reject_code (default: 450)
       The numerical Postfix SMTP server response code when a  sender  or  recipient  address  is
       rejected  by  the reject_unknown_sender_domain or reject_unknown_recipient_domain restric-
       tion.  The response is always 450 in case of a temporary DNS error.

       Do not change this unless you have a complete understanding of RFC 5321.

unknown_address_tempfail_action (default: $reject_tempfail_action)
       The    Postfix	 SMTP	 server's    action    when    reject_unknown_sender_domain    or
       reject_unknown_recipient_domain	fail  due to a temporary error condition. Specify "defer"
       to defer the remote SMTP client request immediately. With  the  default	"defer_if_permit"
       action,	the  Postfix  SMTP server continues to look for opportunities to reject mail, and
       defers the client request only if it would otherwise be accepted.

       This feature is available in Postfix 2.6 and later.

unknown_client_reject_code (default: 450)
       The numerical Postfix SMTP server response code when a client without  valid  address  <=>
       name  mapping  is  rejected  by	the  reject_unknown_client_hostname restriction. The SMTP
       server always replies with 450 when the mapping failed due to a temporary error condition.

       Do not change this unless you have a complete understanding of RFC 5321.

unknown_helo_hostname_tempfail_action (default: $reject_tempfail_action)
       The Postfix SMTP server's action when reject_unknown_helo_hostname fails due to an  tempo-
       rary error condition. Specify "defer" to defer the remote SMTP client request immediately.
       With the default "defer_if_permit" action, the Postfix SMTP server continues to	look  for
       opportunities  to reject mail, and defers the client request only if it would otherwise be
       accepted.

       This feature is available in Postfix 2.6 and later.

unknown_hostname_reject_code (default: 450)
       The numerical Postfix SMTP server response code when the hostname specified with the  HELO
       or EHLO command is rejected by the reject_unknown_helo_hostname restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

unknown_local_recipient_reject_code (default: 550)
       The  numerical  Postfix	SMTP  server response code when a recipient address is local, and
       $local_recipient_maps specifies a list of lookup tables that does not match the recipient.
       A  recipient address is local when its domain matches $mydestination, $proxy_interfaces or
       $inet_interfaces.

       The default setting is 550 (reject mail) but it is safer to initially use 450  (try  again
       later) so you have time to find out if your local_recipient_maps settings are OK.

       Example:

       unknown_local_recipient_reject_code = 450

       This feature is available in Postfix 2.0 and later.

unknown_relay_recipient_reject_code (default: 550)
       The   numerical	 Postfix  SMTP	server	reply  code  when  a  recipient  address  matches
       $relay_domains, and relay_recipient_maps specifies a list of lookup tables that	does  not
       match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_alias_reject_code (default: 550)
       The   Postfix   SMTP   server   reply   code   when  a  recipient  address  matches  $vir-
       tual_alias_domains, and $virtual_alias_maps specifies a list of lookup  tables  that  does
       not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_mailbox_reject_code (default: 550)
       The  Postfix  SMTP  server  reply  code	when  a  recipient address matches $virtual_mail-
       box_domains, and $virtual_mailbox_maps specifies a list of lookup  tables  that	does  not
       match the recipient address.

       This feature is available in Postfix 2.0 and later.

unverified_recipient_defer_code (default: 450)
       The  numerical  Postfix SMTP server response when a recipient address probe fails due to a
       temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.6 and later.

unverified_recipient_reject_code (default: 450)
       The numerical Postfix SMTP server response when a recipient address  is	rejected  by  the
       reject_unverified_recipient restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.1 and later.

unverified_recipient_reject_reason (default: empty)
       The  Postfix  SMTP server's reply when rejecting mail with reject_unverified_recipient. Do
       not include the numeric SMTP reply code or the  enhanced  status  code.	By  default,  the
       response includes actual address verification details.

       Example:

       unverified_recipient_reject_reason = Recipient address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_recipient_tempfail_action (default: $reject_tempfail_action)
       The Postfix SMTP server's action when reject_unverified_recipient fails due to a temporary
       error condition. Specify "defer" to defer the remote SMTP client request immediately. With
       the default "defer_if_permit" action, the Postfix SMTP server continues to look for oppor-
       tunities to reject mail, and defers the client request  only  if  it  would  otherwise  be
       accepted.

       This feature is available in Postfix 2.6 and later.

unverified_sender_defer_code (default: 450)
       The numerical Postfix SMTP server response code when a sender address probe fails due to a
       temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.6 and later.

unverified_sender_reject_code (default: 450)
       The numerical Postfix SMTP server response code when a recipient address  is  rejected  by
       the reject_unverified_sender restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.1 and later.

unverified_sender_reject_reason (default: empty)
       The  Postfix SMTP server's reply when rejecting mail with reject_unverified_sender. Do not
       include the numeric SMTP reply code or the enhanced status code. By default, the  response
       includes actual address verification details.

       Example:

       unverified_sender_reject_reason = Sender address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_sender_tempfail_action (default: $reject_tempfail_action)
       The  Postfix  SMTP  server's action when reject_unverified_sender fails due to a temporary
       error condition. Specify "defer" to defer the remote SMTP client request immediately. With
       the default "defer_if_permit" action, the Postfix SMTP server continues to look for oppor-
       tunities to reject mail, and defers the client request  only  if  it  would  otherwise  be
       accepted.

       This feature is available in Postfix 2.6 and later.

verp_delimiter_filter (default: -=+)
       The  characters	Postfix  accepts  as VERP delimiter characters on the Postfix sendmail(1)
       command line and in SMTP commands.

       This feature is available in Postfix 1.1 and later.

virtual_alias_domains (default: $virtual_alias_maps)
       Postfix is final destination for the specified list of virtual  alias  domains,	that  is,
       domains for which all addresses are aliased to addresses in other local or remote domains.
       The SMTP server validates recipient addresses with $virtual_alias_maps  and  rejects  non-
       existent  recipients.  See also the virtual alias domain class in the ADDRESS_CLASS_README
       file

       This feature is available in Postfix 2.0 and later. The default value is backwards compat-
       ible with Postfix version 1.1.

       The  default  value is $virtual_alias_maps so that you can keep all information about vir-
       tual alias domains in one place.  If you have many users, it is better to separate  infor-
       mation  that  changes more frequently (virtual address -> local or remote address mapping)
       from information that changes less frequently (the list of virtual domain names).

       Specify a list of host or domain names, "/file/name" or "type:table"  patterns,	separated
       by  commas  and/or  whitespace.	A  "/file/name"  pattern  is  replaced by its contents; a
       "type:table" lookup table is matched when a table  entry  matches  a  lookup  string  (the
       lookup result is ignored).  Continue long lines by starting the next line with whitespace.
       Specify "!pattern" to exclude a host or domain name from the list. The form  "!/file/name"
       is supported only in Postfix version 2.4 and later.

       See also the VIRTUAL_README and ADDRESS_CLASS_README documents for further information.

       Example:

       virtual_alias_domains = virtual1.tld virtual2.tld

virtual_alias_expansion_limit (default: 1000)
       The  maximal  number of addresses that virtual alias expansion produces from each original
       recipient.

       This feature is available in Postfix 2.1 and later.

virtual_alias_maps (default: $virtual_maps)
       Optional lookup tables that alias specific mail addresses or domains  to  other	local  or
       remote  address.   The table format and lookups are documented in virtual(5). For an over-
       view of Postfix address manipulations see the ADDRESS_REWRITING_README document.

       This feature is available in Postfix 2.0 and later. The default value is backwards compat-
       ible with Postfix version 1.1.

       If  you	use  this  feature  with  indexed files, run "postmap /etc/postfix/virtual" after
       changing the file.

       Examples:

       virtual_alias_maps = dbm:/etc/postfix/virtual
       virtual_alias_maps = hash:/etc/postfix/virtual

virtual_alias_recursion_limit (default: 1000)
       The maximal nesting depth of virtual alias expansion.  Currently the  recursion	limit  is
       applied	only  to  the left branch of the expansion graph, so the depth of the tree can in
       the worst case reach the sum of the expansion and recursion limits.  This  may  change  in
       the future.

       This feature is available in Postfix 2.1 and later.

virtual_destination_concurrency_limit (default: $default_destination_concurrency_limit)
       The  maximal number of parallel deliveries to the same destination via the virtual message
       delivery transport. This limit is enforced by the  queue  manager.  The	message  delivery
       transport name is the first field in the entry in the master.cf file.

virtual_destination_recipient_limit (default: $default_destination_recipient_limit)
       The  maximal  number of recipients per message for the virtual message delivery transport.
       This limit is enforced by the queue manager. The message delivery transport  name  is  the
       first field in the entry in the master.cf file.

       Setting	this parameter to a value of 1 changes the meaning of virtual_destination_concur-
       rency_limit from concurrency per domain into concurrency per recipient.

virtual_gid_maps (default: empty)
       Lookup tables with the per-recipient group ID for virtual(8) mailbox delivery.

       This parameter is specific to the virtual(8) delivery agent.  It does not apply when  mail
       is delivered with a different mail delivery program.

       In  a  lookup  table,  specify  a left-hand side of "@domain.tld" to match any user in the
       specified domain that does not have a specific "user@domain.tld" entry.

       When a recipient address has an optional address extension (user+foo@domain.tld), the vir-
       tual(8)	delivery  agent  looks	up  the full address first, and when the lookup fails, it
       looks up the unextended address (user@domain.tld).

       Note 1: for security reasons, the virtual(8) delivery agent disallows  regular  expression
       substitution  of  $1  etc.  in regular expression lookup tables, because that would open a
       security hole.

       Note 2: for security reasons, the virtual(8) delivery agent will silently ignore  requests
       to  use	the  proxymap(8)  server. Instead it will open the table directly. Before Postfix
       version 2.2, the virtual(8) delivery agent will terminate with a fatal error.

virtual_mailbox_base (default: empty)
       A prefix that the virtual(8) delivery agent prepends to all pathname  results  from  $vir-
       tual_mailbox_maps  table  lookups.  This is a safety measure to ensure that an out of con-
       trol map doesn't litter the file system with mailboxes.	While virtual_mailbox_base  could
       be set to "/", this setting isn't recommended.

       This  parameter is specific to the virtual(8) delivery agent.  It does not apply when mail
       is delivered with a different mail delivery program.

       Example:

       virtual_mailbox_base = /var/mail

virtual_mailbox_domains (default: $virtual_mailbox_maps)
       Postfix is final destination for the specified list of domains; mail is delivered via  the
       $virtual_transport  mail  delivery  transport.	By default this is the Postfix virtual(8)
       delivery agent.	The SMTP server validates recipient addresses with  $virtual_mailbox_maps
       and  rejects  mail for non-existent recipients.	See also the virtual mailbox domain class
       in the ADDRESS_CLASS_README file.

       This parameter expects the same syntax as the mydestination configuration parameter.

       This feature is available in Postfix 2.0 and later. The default value is backwards compat-
       ible with Postfix version 1.1.

virtual_mailbox_limit (default: 51200000)
       The maximal size in bytes of an individual virtual(8) mailbox or maildir file, or zero (no
       limit).

       This parameter is specific to the virtual(8) delivery agent.  It does not apply when  mail
       is delivered with a different mail delivery program.

virtual_mailbox_lock (default: see postconf -d output)
       How  to	lock  a  UNIX-style virtual(8) mailbox before attempting delivery.  For a list of
       available file locking methods, use the "postconf -l" command.

       This parameter is specific to the virtual(8) delivery agent.  It does not apply when  mail
       is delivered with a different mail delivery program.

       This  setting  is  ignored  with  maildir style delivery, because such deliveries are safe
       without application-level locks.

       Note 1: the dotlock method requires that the recipient UID or GID has write access to  the
       parent directory of the recipient's mailbox file.

       Note 2: the default setting of this parameter is system dependent.

virtual_mailbox_maps (default: empty)
       Optional  lookup  tables with all valid addresses in the domains that match $virtual_mail-
       box_domains.

       In a lookup table, specify a left-hand side of "@domain.tld" to	match  any  user  in  the
       specified domain that does not have a specific "user@domain.tld" entry.

       The  remainder  of  this  text  is specific to the virtual(8) delivery agent.  It does not
       apply when mail is delivered with a different mail delivery program.

       The virtual(8) delivery agent uses this table to look  up  the  per-recipient  mailbox  or
       maildir	pathname.   If the lookup result ends in a slash ("/"), maildir-style delivery is
       carried out, otherwise the path is assumed to specify a	UNIX-style  mailbox  file.   Note
       that $virtual_mailbox_base is unconditionally prepended to this path.

       When a recipient address has an optional address extension (user+foo@domain.tld), the vir-
       tual(8) delivery agent looks up the full address first, and  when  the  lookup  fails,  it
       looks up the unextended address (user@domain.tld).

       Note  1:  for security reasons, the virtual(8) delivery agent disallows regular expression
       substitution of $1 etc. in regular expression lookup tables, because  that  would  open	a
       security hole.

       Note  2: for security reasons, the virtual(8) delivery agent will silently ignore requests
       to use the proxymap(8) server. Instead it will open the	table  directly.  Before  Postfix
       version 2.2, the virtual(8) delivery agent will terminate with a fatal error.

virtual_maps (default: empty)
       Optional  lookup  tables  with  a) names of domains for which all addresses are aliased to
       addresses in other local or remote domains, and b) addresses that are aliased to addresses
       in other local or remote domains.  Available before Postfix version 2.0. With Postfix ver-
       sion 2.0 and later, this is replaced by separate controls: virtual_alias_domains and  vir-
       tual_alias_maps.

virtual_minimum_uid (default: 100)
       The  minimum  user  ID  value  that the virtual(8) delivery agent accepts as a result from
       $virtual_uid_maps table lookup.	Returned values less than this will be rejected, and  the
       message will be deferred.

       This  parameter is specific to the virtual(8) delivery agent.  It does not apply when mail
       is delivered with a different mail delivery program.

virtual_transport (default: virtual)
       The default mail delivery transport and next-hop destination for final delivery to domains
       listed  with  $virtual_mailbox_domains.	This information can be overruled with the trans-
       port(5) table.

       Specify a string of the form transport:nexthop, where transport is  the	name  of  a  mail
       delivery transport defined in master.cf.  The :nexthop destination is optional; its syntax
       is documented in the manual page of the corresponding delivery agent.

       This feature is available in Postfix 2.0 and later.

virtual_uid_maps (default: empty)
       Lookup tables with the per-recipient user ID that the virtual(8) delivery agent uses while
       writing to the recipient's mailbox.

       This  parameter is specific to the virtual(8) delivery agent.  It does not apply when mail
       is delivered with a different mail delivery program.

       In a lookup table, specify a left-hand side of "@domain.tld" to	match  any  user  in  the
       specified domain that does not have a specific "user@domain.tld" entry.

       When a recipient address has an optional address extension (user+foo@domain.tld), the vir-
       tual(8) delivery agent looks up the full address first, and  when  the  lookup  fails,  it
       looks up the unextended address (user@domain.tld).

       Note  1:  for security reasons, the virtual(8) delivery agent disallows regular expression
       substitution of $1 etc. in regular expression lookup tables, because  that  would  open	a
       security hole.

       Note  2: for security reasons, the virtual(8) delivery agent will silently ignore requests
       to use the proxymap(8) server. Instead it will open the	table  directly.  Before  Postfix
       version 2.2, the virtual(8) delivery agent will terminate with a fatal error.

SEE ALSO
       postconf(1), Postfix configuration parameter maintenance
       master(5), Postfix daemon configuration maintenance

LICENSE
       The Secure Mailer license must be distributed with this software.

AUTHOR(S)
       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

										      POSTCONF(5)
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