I was very puzzled to see Russell Coker write:
Therefore the only acceptable method of dealing with spam is to reject it at the SMTP protocol level. Currently I am not aware of any software that supports Bayesian filtering while the message is being received so that it can be rejected if it appears to be spam, it would be possible to do this (I could write the code myself if I had enough spare time) but AFAIK no-one has done it.
I’ve been doing exactly this with Postfix, amavisd-new and SpamAssassin for many years now with great success, rejecting spams at the SMTP level via Postfix’s pre-queue content_filter mechanism using SpamAssassins Baysian filtering, anti-spam rules and blacklist support.
Unfortunately because Russell is using Blogger and requiring people to register I can’t leave a comment for him (as I’ve no desire to sign up for an account with them just to leave a comment).
Update: Corrected link to point to the actual post on Russells blog that I’m talking about!