Really easy! If you have an SSL certificate, you can setup pop3s, imaps and smtps by editing the following:
POP3: /usr/share/courier-imap/pop3d.pem
IMAP: /usr/share/courier-imap/imapd.pem
First, backup the existing files, then (use vi) remove the KEY And CERTIFICATE and replace them with your own. Once you’ve done this, run:
$ service courier-imap restart
The same thing goes for Qmail, make a backup of /var/qmail/control/servercert.pem, then edit it and replace the exiting certificates with your own. Run:
$ service qmail restart
At this point the server end is setup. You should run a few commands to make sure that everything is a-ok:
$ openssl s_client -connect [host]:993
$ openssl s_client -connect [host]:995
$ openssl s_client -connect [host]:465
Note: email client has to be configured to point to the web server’s hostname. In my case, the hostname is gear-l100.[tld.com] so I point Thunderbird to this hostname, check the box for SSL and I am done. You can also tail the maillog on the Plesk server to find out if your email client is connecting over the secured port:
$ tail -f /usr/local/psa/var/log/maillog
Feb 8 15:02:44 gear-l100 imapd-ssl: IMAP connect from @ [64.*********]INFO: LOGIN, user=user, ip=[64.*********], protocol=IMAP
Enjoy!