Dovecot - IMAP & POP3 Handler

Dovecot is an open-source IMAP and POP3 server for Linux/UNIX-like systems, written primarily with security in mind. Now that Postfix is installed and configured, we need to install postfix to manage the pop and imap protocols, which allow us to recover our emails.

Installation of Dovecot

Dovecot packages are presents in the Ubuntu 18.04 default repositories. We will install it with the mysql support. We will install sieve which is useful because it will automatically put the mails into the corresponding folders. It means that, for each domain, it will create a corresponding folder containing the corresponding folder of a virtual user to store its email files.

apt install dovecot-imapd dovecot-mysql dovecot-managesieved

Configuration of Dovecot

Now go to the folder containing the configuration files.

# cd /etc/dovecot/conf.d

• 10-auth.conf file to modify the connection mechanisms by adding or uncommenting the lines.

  Dovecot uses the system users by default but we use Mysql users

  auth_mechanisms = plain login
  #!include auth-system.conf.ext
  !include auth-sql.conf.ext
  

• auth-sql.conf.ext file for the sql configuration

  passdb {
         driver = sql
         args = /etc/dovecot/dovecot-sql.conf.ext
  }
  userdb {
         driver = static
         args = uid=vmail gid=vmail home=/var/mail/vmail/%d/%n
  }
  

• /etc/dovecot/dovecot-sql.conf.ext to tell dovecot how to connect to the SQL database

  driver = mysql
  connect = host=127.0.0.1 dbname=postfix user=postfix password=postfix-db-password
  password_query = SELECT username,domain,password FROM mailbox WHERE username='%u';
  default_pass_scheme = MD5-CRYPT
  

• 10-mail.conf file to configure the mail location directory

  mail_location = maildir:/var/mail/vmail/%d/%n/Maildir
  mail_privileged_group = mail
  

• 10-master.conf file for the connection to the socket.

  service auth {
          unix_listener auth-userdb {
                  mode = 0600
                  user = vmail
          }
          unix_listener /var/spool/postfix/private/auth {
                  mode = 0660
                  user = postfix
                  group = postfix
          }
          user = dovecot
  }
  

• 15-lda.conf file to indicate sieve in order to automatically organize mail into the corresponding folder

  protocol lda {
  # Space separated list of plugins to load (default is global mail_plugins).
  mail_plugins = $mail_plugins sieve
  }
  

We should give permission if we want that the vmail user can launch dovecot

# chgrp vmail /etc/dovecot/dovecot.conf

Now you can restart the dovecot service

# systemctl restart dovecot

Integrate dovecot to postfix

Now that we have configured dovecot, we should indicate postfix to work with dovecot. Edit the master postfix configuration file(/etc/postfix/master.cf) and add the lines below at the end of the file

dovecot   unix  -       n       n       -       -       pipe
flags=DRhu user=vmail:vmail argv=/usr/lib/dovecot/deliver -f ${sender} -d ${user}@${nexthop}

Now edit the main postfix configuration file (/etc/postfix/main.cf)

# Allow authenticated users to send email, and use Dovecot to authenticate them. Tells Postfix to use Dovecot for authentication
virtual_transport = dovecot
dovecot_destination_recipient_limit = 1
smtpd_sasl_type = dovecot
smtp_sasl_type = dovecot

Then restart postfix

# systemctl restart postfix