Be the first to 
- Spam Sleuth offers precise Bayesian spam filtering
- Can also use powerful scoring filters, blacklists, challenge/response, and more
- Spam Sleuth can work transparently as a POP proxy
- Default setup not ideal, produces false positives
- With way too many options and settings, Spam Sleuth is overwhelming
- Spam Sleuth supports POP accounts only
- Spam Sleuth checks multiple POP accounts for spam either in standalone mode or as a POP proxy.
- Spam is detected using scoring filters that take many criteria into account.
- Spam Sleuth can check blackhole lists of known spammers and block mail using certain charsets.
- Spam Sleuth can also make use of Bayesian filtering for even greater accuracy.
- You can also require new, suspicious senders to authenticate themselves to Spam Sleuth.
- Spam Sleuth can deleted or bounced spam automatically, based on its spam score.
- Optionally, "EMail Stamps" lets you request payment (via PayPal) for entry to your mailbox.
- Spam Sleuth can delete certain (dangerous) types of attachments and scripts automatically.
- Spam Sleuth supports Windows 9x/ME/NT/2000/3/XP.
After a bit of training, Spam Sleuth can identify spam very well and remove it automatically, or bounce it (which I don't recommend), or you can even make marketers pay a fee for entry to your Inbox. Of course, no one will pay, but at least they're removed from your mailbox. In addition to Bayesian statistics, Spam Sleuth applies many scoring filters to catch spam, use advanced challenge/response filtering, query DNS blackhole lists, and a lot more.
Less would certainly have been more in this respect, especially since the multitude of options and possible tweaks makes configuring Spam Sleuth a major, possibly overwhelming task while the default settings aren't ideal: Bayesian filtering is turned off and Spam Sleuth relies on its scoring filters instead, which made quite a few mistakes in my tests. It's also a pity that Spam Sleuth only supports POP accounts.
