Cactus Spam Filter is a free easy-to-use spam blocker. It protects your inbox by learning to detect spam as it's being used. After a short while it has adapted to your personal mailbox and blocks out most of the junk e-mail. Since the filter becomes personal, spammers will not be able to fool it.
Even though this is a brutal, merciless spam killer, no e-mails will get lost unless you delete them. Installation is very simple. No setup is required in your e-mail client; this spam stopper integrates seamlessly with all e-mail clients that use POP3. It has been successfully tested with Microsoft Outlook, Microsoft Outlook Express, Netscape, Opera, Mozilla, Mozilla Thunderbird, Eudora, Pegasus Mail, IncrediMail, Foxmail, POP Peeper, Command Line POP Client, The Bat!, and Phoenix Mail.