Spamfire

Spamfire is the most powerful and complete spam filter for the Macintosh.
Spamfire uses four advanced filter technologies to provide incredibly high accuracy.

Every new Spamfire license includes a renewable 12-month subscription to the Spamfire Filter Update Subscription service, which automatically delivers new filters to Spamfire users to stay ahead of the latest spammer tactics.
Also quickly learns what your email looks like and can stop more than 99% of spam for most users.
Moreover Spamfire Setup Assistant automatically reconfigures your email client to pick up filtered mail from Spamfire (for POP accounts).
Spamfire offers fun revenge features that let you send a message to the spammers.