Howtoforge posted a new howto about setting up virtual users and domains with Postfix, Courier and MySQL under Ubuntu Linux 6.10

This document describes how to install a Postfix mail server that is based on virtual users and domains, i.e. users and domains that are in a MySQL database. I'll also demonstrate the installation and configuration of Courier (Courier-POP3, Courier-IMAP), so that Courier can authenticate against the same MySQL database Postfix uses. The resulting Postfix server is capable of SMTP-AUTH and TLS and quota. In addition to that, this tutorial covers the installation of Amavisd, SpamAssassin and ClamAV so that emails will be scanned for spam and viruses.

Virtual Users And Domains With Postfix, Courier And MySQL (Ubuntu 6.10 Edgy Eft)