Dovecot LMTP and Exim

Exim provides support for LMTP over UNIX sockets using the LMTP transport.

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.

Using LMTP over UNIX Socket

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

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

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

router

local_user:
    transport = dovecot_lmtp
    domains = +local_domains
    driver = manualroute
    # Set IP appropriate to your setup.
    route_list = "* 192.168.1.0 byname"
    #if destination server is the local host enable this
    #self = send

transport

dovecot_lmtp:
    driver = smtp
    #allow suffixes/prefixes (default unset)
    rcpt_include_affixes
    protocol = lmtp
    # Set port appropriate to your setup.
    port = 2525

Stripping Domain

If you are using a userdb which does not have domain names, you may need to add a setting to dovecot.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 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.