K9 is an email filtering application that works in conjunction with your regular POP3 email program and automatically classifies incoming emails as spam (junk email) or non-spam without the need for maintaining dozens of rules or constant updates to be downloaded.

Although K9 is a Bayes theorem-based email classification program, such as Popfile or SpamBayes, it is specifically written to only differentiate between spam (junk) email and good email. It is written in C++ as a native Windows application and thus only works on Windows operating systems.

It uses intelligent statistical analysis that can result in extremely high accuracy over time since K9 learns from its mistakes and becomes better and better at being able to identify spam. More importantly it learns to recognize what you individually consider to be spam.

More information and detailed instructions are available at the K9 homepage. There is also a French version and guides in German, Spanish, Italian, Russian and Swedish (along the English one of course).

Available for:

• Windows

SpamBayes a statistical (Bayesian) anti-spam filter with an emphasis on testing newer approaches to scoring messages. It will classify incoming email messages as ’spam’, ‘ham’ (good, non-spam email) or ‘unsure’. This means you can have spam or unsure messages automatically filed away in a different mail folder, where it won’t interrupt your email reading.

SpamBayes will work with most POP3 or IMAP compatible clients. It flags the messages so that your mailer can handle the different message types. You might set it up so that ham goes straight through untouched, spam goes to a folder that you ignore (or delete without checking) and the unsure messages go to another folder which you can review for errors.

Detailed information and download links are here.

Available for:

• Windows
• MacOS
• Linux

POPFile, a free, open source anti-spam filter,  was one of the first Bayesian filters and is still one of the best. It works as a proxy mail server so that means that it can be used with any POP email client.
As with all Bayesian filters its effectiveness takes a little time to develop as the filter has to be trained to recognize your spam from your normal mail so it may take a week or so before results start becoming accurate and best results may take a month or more.
POPFile is actually an automatic mail classification tool. Once properly set up and trained, it will work in the background of your computer, scanning mail as it arrives and filing it however you wish. You can give it a simple job, like separating out junk e-mail, or a complicated one – like filing mail into a dozen folders. Think of it as a personal assistant for your inbox.
POPFile used to be a recomendation mostly for experienced users, however now it comes in two versions – an easy-to-install Windows version, and a cross-platform version for technically-minded users. Once installed, the two are identical.

Click here to learn more about it and/or download it.

Available for:

• Windows (easy installer)
• Any platform with Perl installed

xTerminator allows you to check your email on your mail server before you download it to your PC saving valuable time and bandwidth.
You can configure it for multiple accounts, to automatically filter unwanted messages while you have the option to manually check messages before deletion, or even to auto accept friends (if they know the answer to a special question). This latest feature, the versatile built-in Challenge/Response System and the improved Quick Learn option makes xTerminator the most feature rich free anti-spam tool I have ever come across (since Mailwasher went commercial).

If you’re still plagued with spam, and looking for a solid solution you should definitely check this program out.

Available for:

• Windows