Dovecot is a Mail Delivery Agent, written with security primarily in mind. It supports the major mailbox formats: mbox or Maildir. This section explain how to set it up as an imap or pop3 server.
To install dovecot, run the following command in the command prompt:
sudo apt-get install dovecot-imapd dovecot-pop3d
To configure dovecot, you can edit the file /etc/dovecot/dovecot.conf. You can choose the protocol you use. It could be pop3, pop3s (pop3 secure), imap and imaps (imap secure). A description of these protocols is beyond the scope of this guide. For further information, refer to the Wikipedia articles on POP3 and IMAP.
IMAPS and POP3S are more secure that the simple IMAP and POP3 because they use SSL encryption to connect. Once you have chosen the protocol, amend the following line in the file /etc/dovecot/dovecot.conf:
protocols = pop3 pop3s imap imaps
Next, choose the mailbox you would like to use. Dovecot supports maildir and mbox formats. These are the most commonly used mailbox formats. They both have their own benefits and are discussed on the Dovecot web site.
Once you have chosen your mailbox type, edit the file /etc/dovecot/conf.d/10-mail.conf and change the following line:
mail_location = maildir:~/Maildir # (for maildir) or mail_location = mbox:~/mail:INBOX=/var/spool/mail/%u # (for mbox)
You should configure your Mail Transport Agent (MTA) to transfer the incoming mail to this type of mailbox if it is different from the one you have configured.
Once you have configured dovecot, restart the dovecot daemon in order to test your setup:
sudo service dovecot restart
If you have enabled imap, or pop3, you can also try to log in with the commands telnet localhost pop3 or telnet localhost imap2. If you see something like the following, the installation has been successful:
bhuvan@rainbow:~$ telnet localhost pop3 Trying 127.0.0.1... Connected to localhost.localdomain. Escape character is '^]'. +OK Dovecot ready.
Dovecot SSL Configuration
To configure dovecot to use SSL, you can edit the file /etc/dovecot/conf.d/10-ssl.conf and amend following lines:
ssl = yes ssl_cert = </etc/ssl/certs/dovecot.pem ssl_key = </etc/ssl/private/dovecot.pem
You can get the SSL certificate from a Certificate Issuing Authority or you can create self signed SSL certificate. The latter is a good option for email, because SMTP clients rarely complain about "self-signed certificates". Please refer to Certificates for details about how to create self signed SSL certificate. Once you create the certificate, you will have a key file and a certificate file. Please copy them to the location pointed in the /etc/dovecot/conf.d/10-ssl.conf configuration file.
Firewall Configuration for an Email Server
To access your mail server from another computer, you must configure your firewall to allow connections to the server on the necessary ports.
IMAP - 143
IMAPS - 993
POP3 - 110
POP3S - 995