Debian-Administration have recently had two articles about mail administration using procmail and postfix.
Filtering mail with procmail:
If you are like me you receive a lot of incoming email, too much to leave in one mailbox. Using the procmail tool you can apply filters to split your mail up into different boxes – or apply almost limitless processing to incoming mail.
Handling email for multiple virtual domains is a common server task. Here we'll show how easy that is to manage using the postfix mailserver using just a couple of small configuration changes.