Mailwasher - Over 8 million people use MailWasher as their spam filter
Spamfence.net - Professional e-mail security free for private use: With Spamfence.
SpamAssassin - Use this program to "Unspam" your mailbox(es).
SpamSieve - Save time by adding powerful spam filtering to the e-mail client on your Mac.
Symantec Email Security.cloud - Symantec Email Security.cloud provides always-on, inbound and outbound email security against malware, targeted attacks, and advanced threats
POPFile - POPFile classifies email into categories you define.