SpamSieve implements a powerful Bayesian filter whose performance is far superior to any included in other email clients. It’s compatible with Apple Mail, Emailer, Entourage, Eudora, GyazMail, Mailsmith, Outlook Express, PowerMail, and Thunderbird.
Another interesting feature in SpamSieve is its ability to integrate with Address Book. This prevents all emails from existing contacts from being marked as spam. The same applies for address books in Eudora and Entourage.
In addition, it’s capable of deciphering the content of spam messages with special coding and compiling diverse information about its effectiveness.