The programs below are free email spam filter software solutions with no limitation:

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- Spam Terrier – Free email spam filter from Agnitum, the maker of Outpost Firewall. Spam Terrier features a self-learning anti-spam engine, integration to email programs, behavior-driven detection and options to whitelist and blacklist. System Requirements: XP, Vista, Windows 2000, Windows Server 2003/2008.
- G-Lock SpamCombat – Free email spam filtering of POP3 and IMAP accounts. SpamCombat lets you block spam by country of origin, delete spam from email servers, and recover deleted emails. SpamCombat uses Bayesian, whitelist, blacklist, HTML validator, and a DNSBL filter. System Requirements: Windows 95, 98, 2000, XP, NT, Vista, and Windows 7.
- Spamato – A free email plug-in for Microsoft Outlook,Thunderbird, Mozilla Mail in Windows XP, Vista, and Windows 7. It can also be used in Outlook Express, Incredimail, and Eudora email programs by installing Spamtoxy. It uses several spam blockers such as Bayesian, Comha, Domainator, Earlgrey, etc. Other system requirements: Sun Java Runtime Environment.

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- Comodo AntiSpam – The free anti-spam from the maker of Comodo Firewall features pro-active spam defense to report spam to the postmaster of the spammer’s domain. The program supports Outlook, Outlook Express and any other POP3/SMTP-based email software. System requirements: Windows 2000 and XP. Please note that a computer restart is required after installing Comodo AntiSpam.
- SpamBayes – An open-source Bayesian spam filter with support to Outlook, Windows Live Mail, Thunderbird, and other email clients for Windows. SpamBayes classifies unwanted emails as 'spam,' or 'ham' for good emails and 'unsure' if undetermined.
- Spamihilator – Free spam filtering for POP3 and IMAP accounts. It comes with an option to use secure connection over SSL/TLS. Spam is recognized using learning filters and a DCC network to recognize bulk spam email. Spamihilator works with Outlook, Outlook Express, Thunderbird, Pegasus, Opera, Eudora, and other email program. System Requirements: Windows 2000, XP, Windows 2003, Vista, and Windows 7.
- POPFile - Anti-spam for Windows 7, Vista, XP, and Mac OS X. POPFile automatically classifies and sorts messages into spam and not spam, after set up and training.
Screenshots (Donna Buenaventura), Mailwasher Free Website (http://www.mailwasher.net), Spam Terrier (http://www.agnitum.com/products/spam-terrier/screens.php)