Install & Config Dovecot
From: https://ubuntu.com/server/docs/install-and-configure-dovecot 





Install and configure Dovecot




Install Dovecot
To install a basic Dovecot server with common POP3 and IMAP functions, run
the following command:
	sudo apt install dovecot-imapd dovecot-pop3d

There are various other Dovecot modules including dovecot-sieve (mail
filtering), dovecot-solr (full text search), dovecot-antispam (spam filter
training), dovecot-ldap (user directory).




Configure Dovecot
To configure Dovecot, edit the file /etc/dovecot/dovecot.conf and its
included config files in /etc/dovecot/conf.d/. By default, all installed
protocols will be enabled via an include directive in
/etc/dovecot/dovecot.conf.
	!include_try /usr/share/dovecot/protocols.d/*.protocol

IMAPS and POP3S are more secure because they use SSL encryption to connect.
A basic self-signed SSL certificate is automatically set up by package 
ssl-cert and used by Dovecot in /etc/dovecot/conf.d/10-ssl.conf.

Mbox format is configured by default, but you can also use Maildir if
required. More details can be found in the comments in
/etc/dovecot/conf.d/10-mail.conf. Also see the Dovecot web site to learn
about further benefits and details.

Make sure to also configure your chosen Mail Transport Agent (MTA) to
transfer the incoming mail to the selected type of mailbox.




Restart the Dovecot daemon
Once you have configured Dovecot, restart its daemon in order to test your
setup using the following command:
	sudo service dovecot restart

Try to log in with the commands telnet localhost pop3 (for POP3) or telnet
localhost imap2 (for IMAP). You should see something like the following:
	bhuvan@rainbow:~$ telnet localhost pop3
Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.
+OK Dovecot ready.




Dovecot SSL configuration
By default, Dovecot is configured to use SSL automatically using the package
ssl-cert which provides a self signed certificate.

You can instead generate your own custom certificate for Dovecot using
openssh, for example:
	sudo openssl req -new -x509 -days 1000 -nodes -out "/etc/dovecot/dovecot.pem" \
 -keyout "/etc/dovecot/private/dovecot.pem"

Next, edit /etc/dovecot/conf.d/10-ssl.conf and amend following lines to
specify that Dovecot should use these custom certificates :
	ssl_cert = </etc/dovecot/private/dovecot.pem
ssl_key = </etc/dovecot/private/dovecot.key

You can get the SSL certificate from a Certificate Issuing Authority or you can 
create self-signed one. Once you create the certificate, you will have a key
file and a certificate file that you want to make known in the config shown above.




Further reading:
 For more details on creating custom certificates, see our guide on 
security certificates.
	Configure a firewall 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.





References