Please do not confuse my K9 application with the comparatively recent K-9 Mail app for the Android operating system. It is unfortunate (or maybe intentional?) that they decided to call their email application by the same name when mine had been available and popular for several years prior to its existence. For the Android app, K-9 Mail, please go here.

My K9 program for Windows has not been updated in many years. However, plenty of people still use it and have great success with it. No support or email questions will be answered for this software since no further development is planned.
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. It uses intelligent statistical analysis that can result in extremely high accuracy over time.

K9 learns from its mistakes and becomes better and better at being able to identify spam. More importantly it learns to recognize what you consider to be spam.

K9 is for standard POP3 email accounts only. It does not support IMAP nor does it support Hotmail, AOL or any other kind of webmail type systems. It does not natively support SSL or secure authentication.

You can choose to download either the minimalist ZIP file containing the K9 executable only (no installer or uninstaller) or the full installation EXE that will enable you to uninstall the application and all associated files and registry items if you wish to (recommended for first time users). When installing over a previous version you will not lose any information or "learning". K9 does not contain spyware, adware or any kind of malware whatsoever.

The entire KeirNet website contents for K9 is available for download in the form of a Microsoft Compiled HTML (CHM) file. This file includes all of the documentation for K9 shown here and on the following pages. This may be a more convenient format for those who wish to read how to use K9 offline.

Please be aware that this file may not be available at all times due to excessive bandwidth usage!

KeirNet CHM file download (893K)

Thanks to Rob Beekmans we now have a Dutch translation of K9 available!

Thanks to the great work of "Aristot" there is now a French version of K9 available!

du K9 - Dutch ZIP: 13K

fr K9 - French ZIP: 111K

german K9 guide in German. Here

spanish K9 guide in Spanish. Here

italian K9 guide in Italian. Here

russian K9 guide in Russian. Here

swedish K9 quick start guide in Swedish. Here

K9 was written to fill the gap in the Windows freeware statistics-based spam email filtering software market. It was inspired by the words of Paul Graham's A Plan for Spam and the work of John Graham-Cumming and others who created the fantastic POPFile project.

Many thanks to Lim Chee Aun from Phoenity for designing a stunning new set of toolbar icons for K9.

Thanks go to Steve Gibson for providing an area for general discussions about spam on the grc.spam NNTP newsgroup at