What are some alternatives?
EuropeanMX - Protects your company by blocking spam and virus before they reach your network.
Mailwasher - Over 8 million people use MailWasher as their spam filter
Hornetsecurity - Hornetsecurity offers you comprehensive, integrated managed e-mail security services.
POPFile - POPFile classifies email into categories you define.
SpamTitan - SpamTitan is an anti-spam email solution specifically developed to meet the demands of modern business. Delivering a spam detection rate over 99.9%
Spamfence.net - Professional e-mail security free for private use: With Spamfence.