lmtp - Postfix local delivery via LMTP
lmtp [generic Postfix daemon options]
The LMTP client processes message delivery requests from the queue manager. Each request
specifies a queue file, a sender address, a domain or host to deliver to, and recipient
information. This program expects to be run from the master(8) process manager.
The LMTP client updates the queue file and marks recipients as finished, or it informs the
queue manager that delivery should be tried again at a later time. Delivery problem
reports are sent to the bounce(8) or defer(8) daemon as appropriate.
The LMTP client connects to the destination specified in the message delivery request. The
destination, usually specified in the Postfix transport(5) table, has the form:
Connect to the local UNIX-domain server that is bound to the specified pathname. If
the process runs chrooted, an absolute pathname is interpreted relative to the
changed root directory.
inet:host, inet:host:port (symbolic host)
inet:[addr], inet:[addr]:port (numeric host)
Connect to the specified IPV4 TCP port on the specified local or remote host. If no
port is specified, connect to the port defined as lmtp in services(4). If no such
service is found, the lmtp_tcp_port configuration parameter (default value of 24)
will be used.
The LMTP client does not perform MX (mail exchanger) lookups since those are
defined only for mail delivery via SMTP.
If neither unix: nor inet: are specified, inet: is assumed.
The LMTP client is moderately security-sensitive. It talks to LMTP servers and to DNS
servers on the network. The LMTP client can be run chrooted at fixed low privilege.
RFC 821 (SMTP protocol)
RFC 1651 (SMTP service extensions)
RFC 1870 (Message Size Declaration)
RFC 2033 (LMTP protocol)
RFC 2197 (Pipelining)
RFC 2554 (AUTH command)
RFC 2821 (SMTP protocol)
Problems and transactions are logged to syslogd(8). Corrupted message files are marked so
that the queue manager can move them to the corrupt queue for further inspection.
Depending on the setting of the notify_classes parameter, the postmaster is notified of
bounces, protocol problems, and of other trouble.
The following main.cf parameters are especially relevant to this program. See the Postfix
main.cf file for syntax details and for default values. Use the postfix reload command
after a configuration change.
Verbose logging level increment for hosts that match a pattern in the
List of domain or network patterns. When a remote host matches a pattern, increase
the verbose logging level by the amount specified in the debug_peer_level parame-
Recipient of protocol/policy/resource/software error notices.
When this parameter includes the protocol class, send mail to the postmaster with
transcripts of LMTP sessions with protocol errors.
Do not wait for the server response after sending QUIT.
The TCP port to be used when connecting to a LMTP server. Used as backup if the
lmtp service is not found in services(4).
Enable per-session authentication as per RFC 2554 (SASL). By default, Postfix is
built without SASL support.
Lookup tables with per-host or domain name:password entries. No entry for a host
means no attempt to authenticate.
Zero or more of the following.
Disallow authentication methods that use plaintext passwords.
Disallow authentication methods that are vulnerable to non-dictionary active
Disallow authentication methods that are vulnerable to passive dictionary
Disallow anonymous logins.
Should we cache the connection to the LMTP server? The effectiveness of cached con-
nections will be determined by the number of LMTP servers in use, and the concur-
rency limit specified for the LMTP client. Cached connections are closed under any
of the following conditions:
o The 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
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 LMTP server associated with
the current session does not respond to the RSET command.
Limit the number of parallel deliveries to the same destination via this mail
delivery transport. transport is the name of the service as specified in the mas-
ter.cf file. The default limit is taken from the default_destination_concur-
Limit the number of recipients per message delivery via this mail delivery trans-
port. transport is the name of the service as specified in the master.cf file. The
default limit is taken from the default_destination_recipient_limit parameter.
This parameter becomes significant if the LMTP client is used for local delivery.
Some LMTP servers can optimize delivery of the same message to multiple recipients.
The default limit for local mail delivery is 1.
Setting this parameter to 0 will lead to an unbounded number of recipients per
delivery. However, this could be risky since it may make the machine vulnerable to
running out of resources if messages are encountered with an inordinate number of
recipients. Exercise care when setting this parameter.
The default time unit is seconds; an explicit time unit can be specified by appending a
one-letter suffix to the value: s (seconds), m (minutes), h (hours), d (days) or w
Timeout for opening a connection to the LMTP server. If no connection can be made
within the deadline, the message is deferred.
Timeout for sending the LHLO command, and for receiving the server response.
Timeout for sending the MAIL FROM command, and for receiving the server response.
Timeout for sending the RCPT TO command, and for receiving the server response.
Timeout for sending the DATA command, and for receiving the server response.
Timeout for sending the message content.
Timeout for sending the "." command, and for receiving the server response. When no
response is received, a warning is logged that the mail may be delivered multiple
Timeout for sending the RSET command, and for receiving the server response.
Timeout for sending the QUIT command, and for receiving the server response.
bounce(8) non-delivery status reports
local(8) local mail delivery
master(8) process manager
qmgr(8) queue manager
services(4) Internet services and aliases
spawn(8) auxiliary command spawner
syslogd(8) system logging
The Secure Mailer license must be distributed with this software.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Alterations for LMTP by:
Philip A. Prindeville
Additional work on LMTP by:
University of Texas at Dallas
P.O. Box 830688, MC34
Richardson, TX 75083, USA