Install Dovecot LDA and SASL for Postfix Mailserver

The Dovecot LDA is a local delivery agent which takes mail from an MTA and delivers it to a user's mailbox.

Key features :-

1. Mailbox indexing during mail delivery which provides faster mailbox access later.
2. Quota enforcing by a plugin.
3. Sieve language support by a plugin.

Here I will explain how to configure Dovecot as your LDA/MDA having MTA running under Postfix. And also I will cover giving Quota and sieve support to Dovecot.

The Mail server installation can be followed from the link below,
postfix-mailserver

The above documentation uses Postfix itself as LDA and this should be modified as explained below.

First we need to add the following to the master file,

vim /etc/postfix/master.cf

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

Now we need to tell postfix to use dovecot as LDA,

vim /etc/postfix/main.cf

virtual_transport = dovecot
dovecot_destination_recipient_limit = 1


Restart postfix,
/etc/init.d/postfix restart


Edit dovecot.conf and add postmaster mail address,

vim /usr/local/etc/dovecot/dovecot.conf

protocol lda {
  postmaster_address = postmaster@test.com
}


If you don't have any user-specific settings, you can avoid the user_query by using userdb static instead of userdb sql.

vim /usr/local/etc/dovecot/conf.d/auth-sql.conf.ext

 userdb {
 driver = static
 args = uid=dovecot gid=dovecot home=/home/vmail/%u
}

If you need user specific quota support then we need to use userdb sql instead of userdb static.

For that,

userdb {
  driver = sql
  args = /usr/local/etc/dovecot/dovecot-sql.conf.ext
}


We need to set the system UID and GID of the LDA user, dovecot(5000) in my case.

vim /usr/local/etc/dovecot/conf.d/10-mail.conf

 mail_uid = 5000
 mail_gid = 5000

 #Specify the mail folder location

 mail_location = maildir:/home/vmail/%u
 mail_privileged_group = dovecot

Restart Dovecot

/etc/init.d/dovecot restart

We can check the dovecot and postfix configurations using these commands,

doveconf -n
postconf -n

Now Dovecot starts receiving mails from Postfix for local delivery.
Go through the logs for debugging ..

tailf /var/log/mail.log


SASL authentication

The Postfix documentation mentioned in above link uses Cyrus as SASL authentication method. Here I will show you how to configure dovecot for SMTP AUTH.

First check whether postfix is having dovecot sasl support,

postconf -a
cyrus
dovecot

Once you have verified that your installation of Postfix supports Dovecot SASL, it's very simple to configure:

vim /usr/local/etc/dovecot/conf.d/10-master.conf

Added inside service auth,

service auth {

   #Postfix smtp-auth
   unix_listener /var/spool/postfix/private/auth {
   group = postfix
   mode = 0660
   user = postfix
   }
 }

vim /usr/local/etc/dovecot/conf.d/10-auth.conf
 auth_mechanisms = plain login digest-md5 cram-md5
 disable_plaintext_auth = yes

Change Postfix configuration as follows,

vim /etc/postfix/main.cf

 smtpd_sasl_type = dovecot
 smtpd_sasl_path = private/auth
 smtpd_sasl_auth_enable = yes
 smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination

Restart Postfix and Dovecot.

Test Authentication,

telnet localhost 25
ehlo localhost
250-localhost.localdomain
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH PLAIN LOGIN DIGEST-MD5 CRAM-MD5
250-AUTH=PLAIN LOGIN DIGEST-MD5 CRAM-MD5
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
AUTH PLAIN AHJpbkBleGFwbGUuY29tAHJpbg==
235 2.7.0 Authentication successful

Thanks for Reading
Cheers /-