This project focuses on a patch / add-on for qmail, written in C, which makes use of a PostgreSQL as database backend in order to implement an AntiSpam method known as "greylisting".
The idea behind greylisting is to block single-shot spamming attempts by denying SMTP deliveries at the first attempt with an temporary error (DSN code 4.x.x) and therefor requesting further delivery-tries to common email-servers / MTAs.
The actual patch has been in production for over a year on different sites, behaves and performs nicely and like blacklisting reduces resources needed for handling email traffic.
You can already find some pieces of information about greylisting on the projects documentation page.
There some more or less usefull articles around describing all the greylisting stuff in more detail. From a quick search on google I got the following, which may be a good start:- Greylisting by Evan Harris
Since a few weeks there are signs of spammers making use of full-featured MTA's (queuing et al). But things will not simply stop there. In fact some features, which could easily be added to a fully database-driven relaying solution, are still missing. I'm thinking about going another step closer towards a nearly zero administration whitelisting system.
Please feel free to download version 1.2.x from sourceforge mirrors and send me your comments at gunny # at # hoslo # dot # ch.
You will also find a small command-line management application written in Perl at the same location. Thanks to David Elze.
last updated 2005-10-14, Guenther Mair