.. _howto-dovecot_lmtp_exim:

=====================
Dovecot LMTP and Exim
=====================

Exim provides support for LMTP over UNIX sockets using the `LMTP
transport <http://www.exim.org/exim-html-current/doc/html/spec_html/ch-the_lmtp_transport.html>`__,
your distribution may/not provide this, run exim -bV and check for
'lmtp' in 'Transports:'. Support for LMTP over TCP sockets is provided
by the `SMTP
transport <http://www.exim.org/exim-html-current/doc/html/spec_html/ch-the_smtp_transport.html>`__.

Using LMTP over UNIX Socket
===========================

Use this configuration if dovecot runs on the same host as exim.

Example router:

::

   local_user:
           debug_print = "R: local_user for $local_part@$domain"
           driver = accept
           domains = +local_domains
           check_local_user
           transport = dovecot_lmtp
           cannot_route_message = Unknown user

Example transport:

::

   dovecot_lmtp:
           driver = lmtp
           socket = /var/run/dovecot/lmtp
           #maximum number of deliveries per batch, default 1
           batch_max = 200
           #allow suffixes/prefixes (default unset)
           rcpt_include_affixes

Using LMTP over TCP Socket
==========================

Example router:

::

   local_user:
           transport = dovecot_lmtp
           domains = +local_domains
           driver = manualroute
           route_list = "* 192.168.1.0 byname"
           #if destination server is the local host enable this
           #self = send

Set IP and port as appropriate to your setup.

Example transport:

::

   dovecot_lmtp:
           driver = smtp
           #allow suffixes/prefixes (default unset)
           rcpt_include_affixes
           protocol = lmtp
           port = 2525

Striping domain to avoid user unknown / doesn't exist error
===========================================================

If you are using a userdb which does not have domain names, you may need
to add a setting to 20-lmtp.conf

::

   protocol lmtp {
      ...
      # use %n to strip away the domain part
      auth_username_format = %n
   }

Symptoms:

-  Exim says something like "LMTP error after RCPT ... 550 ... User
   doesn't exist user@domain"

-  Dovecot verbose log says something like "auth-worker(9048):
   passwd(user@domain): unknown user"

Verifying recipients using LMTP
===============================

You can use callout verification to avoid accepting mail for addresses
which do not exist in Dovecot. Below is a config snippet which could be
used in acl_smtp_rcpt to achieve this:

::

   deny
           message = invalid recipient
           domains = +local_domains
           !verify = recipient/callout=no_cache

For more information on address verification see `the related section of
the Exim
specification <http://www.exim.org/exim-html-current/doc/html/spec_html/ch-access_control_lists.html#SECTaddressverification>`__.

Delivering mails case insensitively
===================================

**Warning:**\ Just use this setup if all your login names contain only
lower case characters! (On Linux see /etc/adduser.conf under NAME_REGEX
variable).

Exim retains the case of the local part. Dovecot's LMTP *may* fail
looking up an incorrect cased local part in your userdb. You can solve
this problem by extending the *protocol lmtp* section:

::

   protocol lmtp {
      ...
      # use %Ln to strip away the domain part
      auth_username_format = %Lu
   }

(If you don't mind allowing case insensitive logins for dovecot
authentication, you may set *auth_username_format* in the global
configuration accordingly and renounce the above change).

In case you prefer to configure exim to lower case the local part
instead, add a router just before your local delivery router:

::

   lowercase_local:
           debug_print = "R: lower case local_part for local delivery"
           driver = redirect
           redirect_router = local_user
           data = ${lc:${local_part}}

Make sure to reference the name you have chosen for your local delivery
router within *redirect_router*.