I am very excited to see that spamassassin 3 was released today. So far I have it installed on a test system and am having my email filtered through it. So far so good. Its only been filtering for 2 hours now, but it has already done a perfect job determining what is spam and what is not. I think the addition of checking SPF records, and more importantly, the URLs contained in the messages, is a huge improvement over the previous versions. From what I understand just as previous versions checked the hosts the email came from and upped the score if they were relayed via addresses in block lists, there is now a block list of URLs. Thus if a message contains a URL that is known to be in spam, that will increase the score quite a bit.
If all goes well, I plan on upgrading all the spamassassin servers to version 3 later this week. Unfortunately if it does not work well, it will be hard to go back as the new version changes the format of the bayes database which I believe means you can’t go back. At least not with the same bayes database.
As usual you can find plenty more info on SPF and SpamAssassin by searching the web.