Dovecot LDA with Postfix
========================

This page contains only information specific to using LDA with Postfix, see
<LDA.txt> for more information about using the LDA itself.

System users
------------

If you wish you use 'dovecot-lda' for all system users on a single domain mail
host you can do it by editing 'mailbox_command' parameter in

'/etc/postfix/main.cf' (postconf(5) [http://www.postfix.org/postconf.5.html]):

---%<-------------------------------------------------------------------------
mailbox_command = /usr/local/libexec/dovecot/dovecot-lda -f "$SENDER" -a
"$RECIPIENT"
#  or
mailbox_command = /usr/libexec/dovecot/dovecot-lda -f "$SENDER" -a "$RECIPIENT"
#  or
mailbox_command = /usr/lib/dovecot/dovecot-lda -f "$SENDER" -a "$RECIPIENT"
#  or wherever it was installed in your system.
---%<-------------------------------------------------------------------------

Then run 'postfix reload'.

 * This command doesn't do a <userdb> [UserDatabase.txt] lookup. If you want
   that (e.g. for per-user quota lookups) you need to add '-d "$USER"'
   parameter.
 * Postfix runs 'mailbox_command' with both the uid and gid of the destination
   user. This may not allow 'dovecot-lda' to write a lock file in '/var/mail'.
   When this directory is writable by a privileged group (say 'main', see the
   option 'mail_privileged_group'), we can use the setgid permission bit on the
   'dovecot-lda' executable:

   ---%<----------------------------------------------------------------------
      # chgrp mail /usr/lib/dovecot/dovecot-lda
      # chmod 2755 /usr/lib/dovecot/dovecot-lda
   ---%<----------------------------------------------------------------------

   Alas these permission will disappear if you update dovecot. A more robust
   way to do so is to compile a relay program '/etc/postfix/dovecot-lda-relay'
   that has the setgid permission and execs the real 'dovecot-lda'.

   ---%<----------------------------------------------------------------------
      # cd /etc/postfix
      # cat >dovecot-lda-relay.c <<EOF
        #include <unistd.h>
        char *pgm = "/usr/lib/dovecot/dovecot-lda";  /* wherever dovecot-lda is
   located */
        int main{int argc, char**argv) { argv[0]=pgm; execv(pgm,argv); return
   10; }
      EOF
      # gcc -o dovecot-lda-relay dovecot-lda-relay.c
      # chown root:mail dovecot-lda-relay
      # chmod 2755 dovecot-lda-relay
   ---%<----------------------------------------------------------------------

   Then, simply invoke '/etc/postfix/dovecot-lda-relay' instead of
   'dovecot-lda' in 'mailbox_command'.
 * Postfix's 'mailbox_size_limit' setting applies to all files that are written
   via dovecot-lda. The default is 50 MB, so dovecot-lda can't write *any*
   files larger than that, including mbox files or log files. This shows up
   only in Dovecot's logs:

   ---%<----------------------------------------------------------------------
   dovecot-lda(user): write() failed with mbox file /home/user/mail/foo: File
   too large (process was started with ulimit -f limit)
   ---%<----------------------------------------------------------------------

 * If you have trouble seeing anything in Dovecot's logs, see <LDA#Logging>
   [LDA.txt].

Virtual users
-------------

Dovecot LDA is very easy to use on large scale installations with Postfix
virtual domains support, just add a 'dovecot' service in
'/etc/postfix/master.cf' (master(5) [http://www.postfix.org/master.5.html]):

---%<-------------------------------------------------------------------------
dovecot   unix  -       n       n       -       -       pipe
  flags=DRhu user=vmail:vmail argv=/usr/local/libexec/dovecot/dovecot-lda -f
${sender} -d ${recipient}
---%<-------------------------------------------------------------------------

An example using address extensions (ie user+extension@domain.com (don't forget
to define the proper recipient_delimiter in Postfix's main.cf)) to deliver to
the folder 'extension' in your maildir (If you wish to preserve the case of
${extension}, remove the 'hu'flags [http://www.postfix.org/pipe.8.html], and be
sure to utilize <Modifiers> [Variables.txt] in your dovecot.conf for mail
locations and other configuration parameters that are expecting lower case):

---%<-------------------------------------------------------------------------
dovecot unix    -       n       n       -       -      pipe
  flags=DRhu user=vmail:vmail argv=/usr/local/libexec/dovecot/dovecot-lda -f
${sender} -d ${user}@${nexthop} -m ${extension}

# or if you have a INBOX/ namespace prefix:
dovecot unix    -       n       n       -       -      pipe
  flags=DRhu user=vmail:vmail argv=/usr/local/libexec/dovecot/dovecot-lda -f
${sender} -d ${user}@${nexthop} -m INBOX/${extension}
---%<-------------------------------------------------------------------------

This example ignores address extensions (ie user+extension@domain.com delivers
just like user@domain.com ), but still shows the original address for Sieve:

---%<-------------------------------------------------------------------------
dovecot   unix  -       n       n       -       -       pipe
  flags=DRhu user=vmail:vmail argv=/usr/lib/dovecot/dovecot-lda -f ${sender} -a
${original_recipient} -d ${user}@${nexthop}
---%<-------------------------------------------------------------------------

Replace 'vmail' above with your virtual mail user account.

Then set 'virtual_transport' to 'dovecot' in '/etc/postfix/main.cf':

---%<-------------------------------------------------------------------------
dovecot_destination_recipient_limit = 1
virtual_mailbox_domains = your.domain.here
virtual_transport = dovecot
---%<-------------------------------------------------------------------------

And remember to run

---%<-------------------------------------------------------------------------
postfix reload
---%<-------------------------------------------------------------------------

Virtual users with multiple uids/gids
-------------------------------------

If you need multiple uids/gids you'll need to set dovecot-lda setuid root or
invoke it through sudo. See <LDA#multipleuids> [LDA.txt] for how to do this
securely.

Postfix with a NFS mail store
-----------------------------

If you are experiencing problems with dovecot-lda processes hanging when
delivering to an NFS mail store, it's likely that the dovecot-lda process is
hanging while waiting for free locks.  The occurrence of this can be greatly
reduced, if not eradicated, by forcing Postfix to only deliver to the same
recipient one at a time.

---%<-------------------------------------------------------------------------
dovecot_destination_concurrency_limit = 1
---%<-------------------------------------------------------------------------

Prevent backscatter
-------------------

To prevent backscatter you should configure Postfix to reject mail for non
existent recipients.

This is the default behaviour (smtpd_reject_unlisted_recipient = yes) so
there's no need to set "reject_unlisted_recipient" in any of your restriction.
But: Postfix must know if a recipient exists. Depending on how you've
configured Dovecot and Postfix this can be done several ways.

System users
------------

If you only use local system users this is no problem - all valid recipients
can be found in the local password or alias database.

Virtual users (static)
----------------------

When you use virtual users and domains you should maintain a list of valid
recipients. The relevant settings settings are:

*virtual_alias_maps, virtual_mailbox_maps*

For static verification you can maintain the content of the files yourself. For
every recipient or alias you need one entry. Example:

*virtual_alias_maps*

---%<-------------------------------------------------------------------------
name_recipient@example.com  external@example.net
---%<-------------------------------------------------------------------------

*virtual_mailbox_maps*

---%<-------------------------------------------------------------------------
name@example.com  OK
recipient@example.com  available
---%<-------------------------------------------------------------------------

Don't forget to run "postmap" afterwards.

*Info:* if you use the Dovecot LDA or LMTP it doesn't matter what you use
behind the recipient address. Use "OK", the full name of the user or else.

Virtual users (dynamic)
-----------------------

Do you already use a database (MySQL, PostgreSQL) for Dovecot? Use the same
source for Postfix. You only have to to define a valid sql query for Postfix.
Example:

---%<-------------------------------------------------------------------------
virtual_mailbox_maps = proxy:mysql:/etc/postfix/virtual_mailbox_maps.cf
---%<-------------------------------------------------------------------------

*virtual_mailbox_maps.cf*

---%<-------------------------------------------------------------------------
user = mysql-user
password = mysql-password
hosts = unix:/var/run/mysql/mysqld.sock
dbname = mailserver
query = SELECT name FROM mailbox WHERE email='%s'
---%<-------------------------------------------------------------------------

This query will return the value of the filed "name" from table "mailbox" if
the email address of the recipient matches the email from the field "email".
This is enough for Postfix because Postfix must only know if the recipient
exists. The value doesn't matter. When you use a database (or LDAP) there's no
need to manually maintain a file with valid recipients.

*Info:* If you use "relay_domains" instead of "virtual_mailbox_domains" you
have to use "relay_recipient_maps" instead of "virtual_mailbox_maps".

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).

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:* you can not use "reject_unverified_recipient" with "pipe" so this
doesn't work with the Dovecot LDA "deliver".

(This file was created from the wiki on 2019-03-05 04:42)