MailRoute!

Use this program to "Unspam" your mailbox(es). The program can be integrated with the mail server to automatically filter all mail for a site. It can also be run by individual users on their own mailbox and integrates with several mail programs. SpamAssassin is highly configurable; if used as a system-wide filter it can still be configured to support per-user preferences.

amavisd-new is a high-performance interface between mailer (MTA) and content checkers: virus scanners, and/or SpamAssassin. It is written in Perl for maintainability, without paying a significant price for speed. It talks to MTA via (E)SMTP or LMTP, or by using helper programs.

Postini is an E-mail and Web security and archiving service owned by Google since 2007. It provides cloud computing services for filtering e-mail spam and malware (before it is delivered to a client's mail server), offers optional e-mail archiving, and protects client networks from web-borne malware.

Happy Moose is a super-efficient cloud anti-SPAM solution for organizations. It stops up to 99.7% of SPAM, and no false positives. It means that you don't need to sift through your huge "Junk" folder.

Backup MX and E-mail Continuity services so that you never lose any e-mail if your server goes down.

Postgrey is a Postfix policy server implementing greylisting developed by David Schweikert.

SMX – Cloud-Based Email Security. Global carrier-grade email security at the network layer with no software or hardware to install.

Spamina provides mx services and mail filtering.