We (IONET) have just released a free, open-source, client-based anti spam product, at http://www.ionet.co.nz/spam. This uses a 'challenge-response' approach via a pre-mail delivery agent, is fully configurable, suppresses NDRs etc. It's fully described on the site, so could be added to the OpenNTF template - whats the process for that?
Cheers
Peter