How to set up a mail server on a Gnu Linux System

Step by step guide by Ivar Abramsen to install Postfix Ubuntu + Postfix + Courier IMAP + MySQL + Amavisd-new + SpamAssassin + ClamAV + SASL + TLS + Squirrel Mail + Postgrey. Easy to follow how to 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.