Virtual Mailhosting System Guide | Gentoo Linux

For most gentoo users, a simple mail client and fetchmail will do. However, if you're hosting a domain with your system, you'll need a full blown MTA (Mail Transfer Agent). And if you're hosting multiple domains, then you'll definitely need something more robust to handle all of the email for your users. This system was designed to be an elegant solution to that problem.

A virtual mail system needs to be able to handle email for numerous domains with multiple users over a variety of interfaces. This presents some issues that must be dealt with. For instance, what if you have two users on different domains that want the same user name? If you are providing imap access and smtp-auth, how do combine the various authentication daemons into a single system? How do you provide security for the numerous components that comprise the system? How do you manage it all?

This howto will show you how to set up with a mail system capable of handling mail for as many domains as your hardware can handle, supports virtual mail users that don't require shell accounts, has domain specific user names, can authenticate web, imap, smtp, and pop3 clients against a single database, utilizes ssl for transport layer security, has a web interface, can handle mailing lists for any domain on the machine, and is controlled by a nice, central and easy mysql database. ...

http://www.gentoo.org/doc/en/virt-mail-howto.xml