This documentation is for Dovecot v2.x, see wiki1 for v1.x documentation.

LMTP Server

LMTP uses the same settings as LDA, 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-runing process started by Dovecot's master process.

Envelope Addresses

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

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, but you'll need to tell Dovecot LMTP to issue passdb lookups:

lmtp_proxy = yes