LMTP Server
===========

LMTP uses the same settings as <LDA.txt>, as specified in 'conf.d/15-lda.conf'
in example configuration. There is also a bit of extra configuration in
'conf.d/20-lmtp.conf'. The main difference is that the LDA is a short-running
process, started as a binary from command line, while LMTP is a long-running
process started by Dovecot's master process.

Envelope Addresses
------------------

Compared to dovecot-lda parameters, the addresses are taken from:

 * -f / Envelope sender address: This is the MAIL FROM: value from LMTP
   session.
 * -r / Final envelope recipient address: This is the RCPT TO: value from LMTP
   session.
 * -a / Original envelope recipient address: This defaults to same as RCPT TO:
   value, but may be overridden by reading it from a header specified by
   'lda_original_recipient_header' setting.
 * -d / Destination username: This is the same as RCPT TO: value, but with the
   "+extension" part removed when 'recipient_delimiter' setting is set. If
   usernames differ from recipient email addresses, the userdb must handle the
   translation.

Listeners
---------

You can configure LMTP to be listening on TCP or UNIX sockets:

---%<-------------------------------------------------------------------------
# add lmtp to protocols, otherwise its listeners are ignored
protocols = imap pop3 lmtp

service lmtp {
  inet_listener lmtp {
    address = 192.168.0.24 127.0.0.1 ::1
    port = 24
  }

  unix_listener lmtp {
    #mode = 0666
  }
}
---%<-------------------------------------------------------------------------

The UNIX listener on $base_dir/lmtp is enabled by default when protocols
setting contains lmtp.

Security
--------

Unfortunately LMTP process currently needs to run as root, and only temporarily
drop privileges to users. Otherwise it couldn't handle mail deliveries to more
than a single user with different UID. If you're using only a single global
UID/GID, you can improve security by running lmtp processes as that user:

---%<-------------------------------------------------------------------------
service lmtp {
  user = vmail
}
---%<-------------------------------------------------------------------------

LMTP Proxying
-------------

It's possible to use Dovecot LMTP server as a proxy to remote LMTP or SMTP
servers. The configuration is similar to <IMAP/POP3 proxying>
[PasswordDatabase.ExtraFields.Proxy.txt], but you'll need to tell Dovecot LMTP
to issue passdb lookups:

---%<-------------------------------------------------------------------------
lmtp_proxy = yes
---%<-------------------------------------------------------------------------

Performance
-----------

For higher volume sites, it may be desirable to increase the number of active
listener processes.  A range of 5 to 20 is probably good for most sites:

---%<-------------------------------------------------------------------------
service lmtp {
  process_min_avail = 5
}
---%<-------------------------------------------------------------------------

Logging
-------

If you want to store LMTP delivery logs to a different file, you can do it
with:

---%<-------------------------------------------------------------------------
service lmtp {
  executable = lmtp -L
}
protocol lmtp {
  info_log_path = /var/log/dovecot-lmtp.log
}
---%<-------------------------------------------------------------------------

For rawlogs, please see <Debugging.Rawlog.txt>

Plugins
-------

 * Most of the <Dovecot plugins> [Plugins.txt] work with LMTP.
 * Virtual quota can be enforced using <Quota plugin> [Quota.txt].
    * 'lmtp_rcpt_check_quota = yes' enables quota checking already at RCPT TO
      stage. This check isn't done for proxied connections.
 * Sieve language support can be added with the <Pigeonhole Sieve plugin>
   [Pigeonhole.Sieve.txt].

Address extension delivery
--------------------------

To make address extension work with LMTP you must check these variables are set

 * lmtp_save_to_detail_mailbox = yes
 * recipient_delimiter = +

Using LMTP with different MTAs
------------------------------

 * <Postfix> [HowTo.PostfixDovecotLMTP.txt]
 * <Exim> [LMTP.Exim.txt]
 * HALON [http://wiki.halon.se/LMTP]

(This file was created from the wiki on 2019-06-19 12:42)