Usually, you do not need to setup an email server under Linux desktop operating system. Most GUI email clients (such as Thunderbird) supports Gmail POP3 and IMAP configurations. But, how do you send mail via the standard or /usr/bin/mail user agents or a shell script? Programs such as sendmail / postfix / exim can be configured as a gmail smarthost but they are largely overkill for this use.
The Courier mail server is a mail transfer agent (MTA) server that provides ESMTP, IMAP, POP3, webmail, and mailing list services with individual components. But, it is best known for its IMAP / IMAPs and POP3 / POP3s (secure version) server component.
Courier can provides support for both regular UNIX operating system account (stored in /etc/passwd) and virtual mail account managed by third party backends such as OpenLDAP, MySQL and so on.
In this quick tutorial, you will learn about installing Courier IMAP SSL digital certificate.
Explains how to bind Qmail SMTP to particular IP address.