The Bottom Line
- K9 spots spam precisely, no false positives
- User friendly interface
- K9 works with any email client
- K9 configuration could be easier, better organized
- No remote administration, Web interface
- K9 supports POP accounts only
- K9 checks POP accounts for spam either as a standalone app or as a POP proxy.
- K9 uses advanced Bayesian statistical analysis to detect spam.
- Detected spam can be marked in the subject, or K9 adds a custom X-header for further filtering.
- False classifications can be corrected easily, and K9 learns with each correction.
- In addition to statistical filtering, K9 can use flexible custom-built keyword filters.
- K9 keeps detailed statistics about classifications, and emails can be broken down to the word level.
- Detecting (anti-)junk words hidden in HTML, K9 offers some protection against spammers' tricking.
- Optionally, K9 can query one DNS blackhole list for additional spam checking.
- K9 supports Windows 9x/ME/NT/2000/3/XP.
Guide Review - K9 1.28 - Spam Filter
The best thing about K9 is its ability to detect spam almost flawlessly using Bayesian statistics. All it takes is a bit of training in the easy to use interface (the exception being the configuration tab, which is a bit confusing), and you can filter all spam to a special folder automatically.
While K9 can query a DNS blackhole list server for known spammers, I don't recommend turning this feature on. It will add nothing to K9's junk mail detection accuracy but some to the time it takes to classify mail.
Working as a POP proxy, K9 can be used with just about any email client. Unfortunately, this also means K9 is restricted to POP accounts. IMAP users must look elsewhere for advanced spam protection.
In addition to IMAP support, remote administration (maybe via a Web interface) would make a nice enhancement for K9.