A while back I recommended an Outlook plug-in called SpamNet, from Cloudmark. At the time, it was a free tool for Outlook users to block spam, that worked quite reliably. Sadly, it’s no longer free. I get so little spam at work (where my e-mail address is relatively unpublished) that I can’t justify buying a subscription.
Like SpamNet, it can be installed as an Outlook plug-in, and easily used via buttons on Outlook’s toolbar. But the technology behind it is very different, as it uses Bayesian filtering rather than distributed recognition. It’s also different in that the core project and recognition engine is command line-oriented. The Outlook-only plug-in is terrific, but only a side project. It’s not required, and there are plenty of ways for those who use something other than Outlook for e-mail to use SpamBayes.
You can read the review for a thorough look, but my experience was that it was just as easy to install as SpamNet, is extremely effective at blocking spam, and is also having fewer false positives. I think the reason for that is SpamNet uses other people’s spam reports to decide what to block in my Inbox, and there’s a lot of people who just block e-mails they signed up for (newsletters, promos, etc.), rather than unsubscribe from them. Those false reports pollute the knowledge base, and affect my results. Bayesian filtering is exactly the opposite — it only cares what I think is spam.