Joe Kissell at EarthWeb.com has put together a good list of 6 programs Mac users can get to know if spam is becoming a problem.
Pros: Blacklist, whitelist, regular expression matching; image spam filtering; several other filtering options.
Cons: No Bayesian filter; no IMAP support; no direct integration with email clients; cluttered interface; poor documentation.
Price: Free (donations accepted)
Pros: Bayesian filter; regular expressions; wide variety of actions available for suspected spam.
Cons: Complex UI; no universal binary version; nearly two years since last update.
Pros: Bayesian filter; blacklist; whitelist; attachment checking; integrates well with Mail and Entourage.
Cons: Adds lots of extra stuff (of questionable value) to your system; expensive.
Price: $40 (includes one-year subscription to filter updates; renewal costs range from $10 for one year to $35 for a permanent subscription).
Pros: Automated setup for most clients works well; good configuration options.
Cons: Weak IMAP support; poor integration with email clients; ongoing subscription cost is a drag.
Pros: Bayesian filter with adjustable sensitivity; blacklist; whitelist; regular expressions; excellent integration with email clients; nearly invisible operation.
Cons: Limited actions available for suspected spam; some initial manual training required.
Pros: Bayesian filter; whitelist; domain and relay blacklists.
Cons: No IMAP support; limited configuration options; awkward procedure for handling false positives; sketchy documentation.
Check out Joe’s full review for each program, plus his conclusion on which is best here:
Spam Filters for Your Mac: Six Choices – [EarthWeb]