This is a collection of procmail recipes which I use to pre-filter the incoming mail before letting SpamBayes take a crack at it. This combination seems to provide a fairly decent level of protection. Naturally, your mileage may vary.

procmail is a mail processor installed on most Linux systems and used to by the mail server to deliver mail to your mailbox. If your mail server is hosted on linux you may use procmail to remove spam and sort messages before they are placed into your mailbox. If, like me, you prefer to use pine in a shell window to check your e-mail, this type of filtering may be your only defense against spam.

In order to understand these recipes, at least some knowledge of procmail and regular expressions syntax is required. The basics can be learned from procmail man pages and from links on procmail home page. Here is a great procmail documentation project and a library of recipes

Spam filters and other useful procmail recipes

Source: filtering spam with procmail | http://www.benya.com/