Virus Bulletin have done a test of spam blocking applications.

Kaspersky and Message Architect came tops....................

The second edition of the test pitted anti-spam filters against an archived collection of spam messages, and a live stream of email from addresses set up by testers. Products were scored for the percentage of spam messages detected and the number of false positives returned.
The top performers were Kaspersky's Anti-Spam 3.0 and Message Architects' M+ Guardian spam blocker.

Giacom's MessageStream service earned a 'gold' certification, while WebRoot's E-Mail Security, FortiMail and BitDefender Security for Mail Servers all earned 'silver' certifications.
Among the worst performers in the test were ClamAV and Spam Assassin. ModusGate also missed out on earning a certification due to a high rate of false positives.
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