The second Linux.Conf.Au fixit that I want to was the Spam fixit. This was hosted by Tridge and Rusty, although somehow Rusty managed not to be there. There was a lot of lively discussion, as everyone has an opinion on Spam these days.

Initially DCC and Razor type systems were showing a good amount of promise, but these use strong checksums, which are easily defeated by inserting random words into the message. Loose checksums are less easily defeated in this way, but instead can produce higher false positive rates.

Penny black techniques were discussed, which are essentially a requirement that the sender perform a computationally intensive operation before sending the message. The sender can then quickly verify the result, and accept the message. The problem with this technique is that it disadvantages normal mail users more than it does spammers. It'll slow down the rate of spam, but spammers can simple add more trojaned Windows boxes to their network and we're back to the same old problem.

Someone mentioned the sendmail tool "milter sender" which looks very interesting. Milter sender verifies the from address of a message on receipt, and can cause the message to be rejected if the from address is invalid.

One attendee also mentioned that he'd tweaked Spamassasin to assign a slight negative score to messages originating in Australia and a slight positive score to messages originating in "spammy" countries like Korea, Brazil and Nigeria.