Postfix and Dovecot LMTP

Starting with Dovecot 2.x a LMTP-Server has been added.

Basic Configuration

The first step is to enable its stack via /etc/dovecot/dovecot.conf

!include conf.d/*.conf
protocols = imap lmtp

Socket configuration

The actual socket is configured in /etc/dovecot/conf.d/10-master.conf. The LMTP service can be bound to both INET or Unix sockets. In this example a Unix socket is placed inside the Postfix spool with appropriate permissions set:

service lmtp {
 unix_listener /var/spool/postfix/private/dovecot-lmtp {
   group = postfix
   mode = 0600
   user = postfix
  }
}

Note that the socket needs to be placed there because Postfix access is limited to this directory.

Plugin Support

Plugin support can be enabled at protocol level via /etc/dovecot/conf.d/20-lmtp.conf, for Quota and Sieve here:

protocol lmtp {
  postmaster_address = postmaster@domainname   # required
  mail_plugins = quota sieve
}

Postfix main.cf Configuration

The final step is to tell Postfix to use this socket for final delivery, in this case in a virtual user scenario:

virtual_transport = lmtp:unix:private/dovecot-lmtp

For a non virtual user setup ( as when mail_location = maildir:~/.maildir ) :

mailbox_transport = lmtp:unix:private/dovecot-lmtp

Dynamic address verification with LMTP

With Dovecot 2.0 you can also use LMTP and the Postfix setting “reject_unverified_recipient” for dynamic address verification. It’s really nice because Postfix doesn’t need to query an external datasource (MySQL, LDAP…). Postfix maintain a local database with existing/non existing addresses (you can configure how long positive/negative results should be cached). Postfix reject_unverified_recipient

To use LMTP and dynamic address verification you must first get Dovecot working. Then you can configure Postfix to use LMTP and set “reject_unverified_recipient” in the smtpd_recipient_restrictions.

On every incoming email Postfix will probe if the recipient address exists. You will see similar entries in your logfile:

Recipient address rejected: undeliverable address: host tux.example.com[private/dovecot-lmtp] said: 550 5.1.1 < tzknvtr@example.com > User doesn't exist: tzknvtr@example.com (in reply to RCPT TO command); from=< cnrilrgfclra@spammer.org > to=< tzknvtr@example.com >

If the recipient address exists (status=deliverable) Postfix accepts the mail.

Info: To eliminate this error put: