sendmail(8) System Manager's Manual sendmail(8)
sendmail, newaliases, mailq, smtpd - Sends mail over the Internet
/usr/sbin/sendmail [-flags] [address ...]
Set the body type to type. The current values are "7BIT" or "8BITMIME" Goes into ARPANET mode. All input lines must end with a CR-LF, and
all messages will be generated with a CR-LF at the end. Also, the From: and Sender: fields are examined for the name of the sender. Runs
as a daemon. This requires Berkeley Interprocess Communications (IPC). The sendmail command will fork and run in the background, listen-
ing on the socket specified in the /etc/services file for incoming SMTP (Simple Mail Transfer Protocol) connections. This is normally run
when going to multiuser mode.
Using this flag is equivalent to invoking sendmail as smtpd. Initializes the alias database. This is the same as invoking the
newaliases command. Delivers mail in the usual way (default). Prints a listing of the queue. This is the same as invoking the
mailq command. Use the SMTP protocol as described in RFC821 on standard input and output. This flag implies all the operations of
the -ba flag that are compatible with SMTP. Runs in address test mode. This mode reads addresses and shows the steps in parsing;
it is used for debugging configuration tables. Verifies names only. Does not try to collect or deliver a message. Verify mode is
normally used for validating users or mailing lists. Uses alternate configuration file. The sendmail command refuses to run as
root if an alternate configuration file is specified. Sets debugging value to X. A useful value is 21.n, where n is any nonzero
integer less than 100. This produces information regarding address parsing and is typically used with the -bt flag. Higher values
of n produce more verbose information. Sets the full name of the sender. Sets the name of the From: user field (that is, the
sender of the mail). The -f flag can only be used by trusted users (normally root, daemon, and network) or if the person you are
trying to become is the same as the person you are. Sets the hop count to N. The hop count is incremented every time the mail is
processed. When it reaches a limit, the mail is returned with an error message, the victim of an aliasing loop. If not specified,
Received lines in the message are counted. The maximum hop count is configurable, but defaults to 30 if you do not configure an
alternate value. The default value is acceptable in most installations but you may want to increase the value if too many messages
are being lost Defines Macro to have Value. This option is normally used only from the sendmail daemon command line. Does not do
aliasing or forwarding. Sets option to the specified value. This form uses long names. Processing flags specified with -O are
described in the Sendmail Installation and Operation Guide on the Documentation CD-ROM. Sets option X to the specified value. Pro-
cessing flags specified with -o are described in the Processing Flags section later in this reference page. Set the name of the
protocol used to receive the message. This can be a simple protocol name such as UUCP or a protocol and hostname, such as UUCP:ucb-
vax. Processes saved messages in the queue at given intervals. If time is omitted, processes the queue once. The time command is
given as a tagged number, with s being seconds, m being minutes, h being hours, d being days, and w being weeks. For example,
-q1h30m or -q90m would both set the time-out to 1 hour and 30 minutes. If the time command is specified, the sendmail command will
run in background mode. This flag can be used safely with -bd. Limit processed jobs to those containing substr as a substring of
the queue ID. Limit processed jobs to those containing substr as a substring of one of the recipients. Limit processed jobs to
those containing substr as a substring of the sender. An alternate and obsolete form of the -f flag. Reads a message for recipi-
ents. The To:, Cc:, and Bcc: lines will be scanned for recipient addresses. The Bcc: line will be deleted before transmission.
Any addresses in the argument list will be suppressed; that is, they will not receive copies even if listed in the message header.
Goes into verbose mode. Alias expansions will be announced, and so forth. Log all traffic in and out of mailers in the indicated
log file. This should only be used as a last resort for debugging mailer bugs. It will log a lot of data very quickly.
The sendmail command sends a message to one or more recipients, routing the message over whatever networks are necessary. The sendmail
command does internetwork forwarding as necessary to deliver the message to the correct place.
The sendmail command is not intended as a user interface routine. Other programs provide user-friendly front ends; sendmail is used only
to deliver preformatted messages.
With no flags, sendmail reads its standard input up to an End-of-File or to a line consisting only of a single . (dot), and sends a copy of
the message found there to all of the addresses listed. It determines the network(s) to use based on the syntax and contents of the
Local addresses are looked up in a file and aliased appropriately. Aliasing can be prevented by preceding the address with a (back-
slash). Normally the sender is not included in any alias expansions; for example, if john sends to group, and group includes john in the
expansion, then the letter will not be delivered to john.
For additional information on mail, see the sendmail book by O'Reilly & Associates and the Sendmail Installation and Operation Guide. The
latter is available on the Documentation CD-ROM.
Processing Option Flags
There are a number of optional sendmail processing flags that can be set. Normally, these will be used only by a system administrator.
They can be set either on the command line using the -o flag or in the configuration file. (Refer to the sendmail.cf reference page for
details on the sendmail.cf file.)
The processing flags are as follows. Note that this is a partial list limited to those options that are likely to be useful on the command
line. For a complete listing, see the Sendmail Installation and Operation Guide.
Full pathname to the alias file. The minimum number of free blocks (bminblocks) needed on the spool filesystem. Sets the blank substitu-
tion character to the character specified in the Character parameter. The sendmail daemon replaces unquoted spaces in addresses with Char-
acter. The supplied configuration file uses the . (dot) for Character. Causes sendmail to queue messages for that mailer daemon without
sending them if an outgoing mailer is marked as expensive to use. The queue can be run when costs are lower or when the queue is large
enough to send the message efficiently. Sets the delivery mode to x. Delivery modes are i for interactive (synchronous) delivery, b for
background (asynchronous) delivery, and q for queue only (that is, actual delivery is done the next time the queue is run). Tries to auto-
matically rebuild the alias database if necessary. Sets error processing to mode x. Valid modes are the following: Mails the error mes-
sage to the user's mailbox, but always exits with a 0 (zero) exit status (normal return). Mails the error message to the user's mailbox.
Displays the error message on the terminal (default). Throws away the error message and returns the exit status only. Writes the error
message to the terminal or mails it if the user is not logged in.
If the text of the message is not mailed by modes m or w and if the sender is a local user, a copy of the message is appended to the
dead.letter file in the sender's home directory. The mode to use when creating temporary files. Saves UNIX compatible style From:
lines at the front of messages. Enables GECOS fuzzy-logic name matching.
The GECOS fields is a field in the /etc/passwd file that usually contains the user's full name. You can modify this information by
using the chfn routine. If sendmail does not find an exact match for the user name, the Match-GECOS option tries to match the user
name against names in the /etc/passwd file.
For example, if user Jane Q. Public's user name is jpq, she will receive mail sent to jane, if she is the only Jane in the
/etc/passwd file. Likewise, if John Doe's username is jd, he will receive mail sent to doe, if he is the only Doe in the
The sendmail Version 8 command and previous versions of sendmail differ in how they process GECOS information. If the GECOS option
is enabled, sendmail Version 8 is very stringent; it requires a match on the entire name. For instance, if the GECOS field for user
jd is "John Doe", then sendmail Version 8 will only work for mail sent to john doe. An older version of sendmail may work with john
doe, john, or doe assuming that this is the only john (or the only doe) in the file. The default group ID to use when calling mail-
ers. The SMTP help file. Specifies the maximum hop count.
The maximum hop count option specifies the maximum number of machines that a mail message can be sent to before it is rejected.
This limit is used to help prevent infinite mail loops. The default is 30. Depending on the size of your mail system, you may
require a higher or lower minimum hop count. Does not interpret a . (dot) on a line by itself as a message terminator. Removes the
excess dot inserted by a remote mailer at the beginning of a line if mail is received through SMTP. In addition, if receiving mail
through SMTP, any dot at the front of a line followed by another dot is removed. This is the opposite of the action performed by
the X mailer flag. Indicate that sendmail should use the Internet domain name server if it can. Send error messages in Multipur-
pose Internet Mail Extension (MIME) format. Set connection cache time out. Set connection cache size. Specifies the log level to
be the value supplied in the number argument. Each number includes the activities of all numbers of lesser value and adds the
activity that it represents. Valid levels and the activities that they represent are as follows: Prevents logging. Logs major
problems only. Logs message collections and failed deliveries. Logs successful deliveries. Logs messages deferred (for example,
because the host is down). Logs messages that are placed in the queue (normal event). Logs unusual but benign incidents (for exam-
ple, trying to process a locked file). Logs the internal queue ID to external message ID mappings (the default). This can be use-
ful for tracing a message as it travels between several hosts. Logs messages that are of interest when debugging. Logs verbose
information regarding the queue. If the sender uses an alias, and that sender is a member of the group named by the alias, then
also send to the sender. Validates the right-hand side of alias rewrite rules when the sendmail daemon performs the newaliases
function. If set, this message may have old style headers. If not set, this message is guaranteed to have new style headers (that
is, commas instead of spaces between addresses). If set, an adaptive algorithm is used that will correctly determine the header
format in most cases. Identifies the person who is to receive a copy of all returned mail. Selects the directory in which to queue
messages. The directory will be created if it does not exist. The time-out on reads. If none is set, sendmail will wait forever
for a mailer. This flag violates the word (if not the intent) of the SMTP specification, so the time-out should probably be fairly
The sendmail Version 8 command has additional fine-grained control of timeouts. See the Sendmail Installation and Operation Guide on
the Documentation CD-ROM for additional information. Saves statistics in the named file. Statistics are only collected if the file
exists. This file must be created by the user. The recommended path for this is /var/adm/sendmail/sendmail.st. Statistics can be
printed out using /usr/sbin/mailstats. Always instantiates the queue file, even under circumstances where it is not strictly neces-
sary. This provides safety against system crashes during delivery. Sets the time-out on undelivered messages in the queue to the
specified time. After delivery has failed (for example, because of a host being down) for this amount of time, failed messages will
be returned to the sender. The default in the configuration file is 3 days. Sets the name of the time zone. Sets the default user
ID for mailers. Runs in verbose mode. The sendmail daemon delivers each message in the mail queue from a separate process. This
option is not required; it can increase system overhead in this environment.
In aliases, the first character of a name can be a vertical bar to cause interpretation of the rest of the name as a command to pipe the
mail to. It may be necessary to quote the name to keep sendmail from suppressing the blanks from between arguments. For example, a file
can contain a common alias such as: msgs: "|/usr/bin/msgs -s"
Aliases can also have the syntax :include:filename to ask sendmail to read the named file for a list of recipients. For example, an alias
such as: poets: :include:/usr/local/lib/poets.list reads /usr/local/lib/poets.list for the list of addresses making up the group.
You can also use the Network Information Service (NIS) to distribute your aliases to other systems.
The sendmail command returns an exit status describing what it did. The codes are defined in <sysexits.h>: Successful completion on all
addresses. The username was not recognized. A catchall meaning necessary resources were not available. There is a syntax error in the
address. There is an internal software error, including bad arguments. There is a temporary operating system error, such as cannot fork.
The hostname was not recognized. The message could not be sent immediately, but was queued.
Links to sendmail
Three additional commands are links to sendmail: Prints the contents of the mail queue. This command is the same as running sendmail with
the -bp flag. Builds a new copy of the alias database from the /var/adm/sendmail/aliases file. This command is the same as running send-
mail with the -bi flag. Runs sendmail as a daemon. This command is equivalent to invoking sendmail with the -bd flag.
Mail addresses are based on the domain address (Internet) protocol. These addresses have the form: email@example.com
Note that the configuration file provided with sendmail specifies that blanks in addresses be converted to dots before being transmitted.
This convention follows the Internet mail protocol described in RFC822, but does not match the Internet mail protocol described in RFC733
(NIC41952). You can change this setting by setting the OB flag in the sendmail configuration file (see the sendmail.cf(4) reference page).
A domain is a logical grouping of systems that are connected together by physical network links. No direct relationship exists between the
actual physical interconnections and the way in which the systems are grouped in the domain. The domain name identifies a specific domain
within a larger group of domains. The domain name has the format of a tree structure. Each node (or leaf) on the tree corresponds to a
resource set, and each node can create and contain new domains below it. The actual domain name of a node is the path from the root of the
tree to that node.
For example, if node hera is part of the domain OSF, which is in turn a subdomain of ORG, a message sent to user geo at that address, uses
this format: geo@hera.OSF.ORG
The message router (usually sendmail) must determine how to send the message to its final destination. If the router is at hera, it deliv-
ers the message to user geo. If the router is at another system within the OSF domain, it corresponds with the name server for that domain
to find out how to deliver the message. If the router is not a part of the OSF domain but is in a domain that is under the ORG domain, it
corresponds with the name server for the ORG domain to find out how to deliver the message. The respective name server returns a network
address to the router. That network address determines the actual path that the message takes to its destination.
The domain address is read from right to left, with each domain in the address separated from the next domain by a . (dot). This format
does not imply any routing. Thus, although the example is specified as an ORG address, the message might actually travel by a different
route if that were more convenient or efficient. At one site, the message associated with the sample address goes directly from the sender
to node hera over a local area network. At another site, it might be sent over a UUCP network or a combination of other delivery methods.
Normally, the actual routing of a message is handled automatically. However, you can route the message manually through several specified
hosts to get it to its final destination. An address using intermediate hosts, called a route address, has the following form:
Explicitly specifying the message routing with these route addresses, while supported, is strongly discouraged by RFC 1123. Instead, allow
the mail software (for example sendmail) to handle routing issues.
This address specifies that the message goes first to the remote system represented by hosta, then to the remote system represented by
hostb, and finally to the remote system represented by hostc. This path is forced even if there is a more efficient route to hostc.
In some cases you may abbreviate the address rather than entering the entire domain name. In general, systems in the same domain do not
need to use the full domain name. For example, a user on node zeus.XYZ.COM can send a message to geo@hera.XYZ.COM by entering only
geo@hera because they are in the same local domain, XYZ.COM.
Other mail address formats exist and the mail routing program (sendmail) converts most of these other formats to a format that the network
routing system can use. However, if you use the domain address format, the routing program operates more efficiently.
For example, if sendmail receives an address in the following format: @host:user it converts it to the corresponding domain address format:
Similarly, if sendmail receives an address in the following format: host!user the mail routing program routes the message directly to the
uucp command. However, when sending mail via uucp, you must include a route address that indicates which UUCP host(s) to send the message
through to get to the final destination.
To route messages through the UUCP network, use one of the following domain address formats. Your choice depends on the way in which the
systems at your site are connected: @system_name.domain_name:uucp-route!user-ID
For example, the address: @zeus:hera!amy sends a message to user amy on UUCP host hera by way of system zeus. The address:
@apollo.802:merlin!lgh sends a message to user lgh on UUCP host merlin via system apollo under the local domain 802. uucp-
In this case, the address: firstname.lastname@example.org sends a message to user amy on system hera under domain 802 via the UUCP link
merlin through arthur. system_name.domain_name:uucp-route:!user-ID@system_namedomain_name
In this example, the address: @apollo.802:email@example.com sends a message to user amy on system hera under domain 802
that first goes through apollo, the gateway node for domain 802, and then through the UUCP link merlin through arthur. (Including
802 in this example is optional because the two domain names are identical.) hosta!hostb!hostc!user
This example is a purely UUCP route address. zeus!hera!kronos!amy sends a message to amy on kronos via the UUCP link zeus through
This example, like the previous one, is a purely UUCP route address. @zeus.UUCP:@hera.UUCP:amy@kronos.UUCP sends a message to amy
on kronos via the UUCP link zeus through hera.
Your host may also be configured to handle DECnet addresses. Under DECnet Phase IV, an address is of the form nodename::username
This is typically converted into a "domain'ized" form, such as firstname.lastname@example.org (parent-domain is something such as
dec.com or OSF.ORG that uniquely identifies your company). Similarly, your host may also handle Phase V type addresses, such as
By default, Tru64 UNIX's sendmail software uses message encoding that uses 8 bits of each byte. Although 8-bit encoding better supports the
full range of characters in many non-English languages, 8-bit encoding is not generally recommended because it violates the SMTP protocol
used for mail transmission over a TCP/IP network.
Specifies the command path. The configuration file. The raw data for alias names. Sets the option variable A to the full pathname of the
aliases file (/var/adm/sendmail/aliases). This file and the aliases.dir file comprise the database of alias names. This file and the
aliases.pag file comprise the database of alias names. This file specifies the users who should receive mail on the local host.
This option is not supported in Tru64 UNIX. The help file. The collected statistics. The mail queue directory.
Except for /usr/sbin/sendmail and /var/adm/sendmail.cf, the previous pathnames are all specified in the /var/adm/sendmail.cf file, so they
may vary on your system.
The process id of the daemon.
Commands: mail(1), mailx(1), rc0(8)
Files: aliases(4), forward(4), sendmail.cf(4)
Specifications: RFC819, RFC821, RFC822 delim off