At a Glance
This absolutely free, open-source spam filter works with Outlook or any other e-mail client software that uses the POP3 or IMAP protocols.
Like many commercial anti-spam utilities, SpamBayes uses Bayesian statistics, rather than lists of keywords, to sort the good mail from the bad, resulting in high rates of spam detection, and very low numbers of false positives--good messages mistaken for spam.
The only thing that seems to slip by SpamBayes with any consistency is the new generation of image-based spam. Perhaps the program's volunteer authors will address that in a forthcoming 1.1 version.