From the page:
How to set up a mail server on a GNU / Linux system
Step by step guide to install Postfix
Ubuntu + Postfix + Courier IMAP + MySQL + Amavisd-new + SpamAssassin + ClamAV + SASL + TLS + SquirrelMail + Postgrey
Easy to follow howto on setting up a mail server with unlimited users and domains, with IMAP/Pop access, anti-spam, anti-virus, secure authentication, encrypted traffic, web mail interface and more.
Based on an Ubuntu distribution platform, but instructions are distro generic.