From Message Partners:
MPP is an enterprise grade email filtering solution for Xserve email servers (not for email clients or home users). MPP now has the most advanced antispam engine available for for Xserve. Install MPP on your Xserve email server and you will see an instant improvement in spam detection. Besides spam filtering MPP offers virus protection, content filtering, email archival, attachment stripping, attachment blocking and more. MPP includes a web-based system for spam quarantine and archive review. MPP is available as a VMWare virtual appliance, supported under VMWare Fusion, or as software to install directly on your email server. The MPP bundle installer installs all components and configures your system to work with MPP automatically.
This review was originally posted on VersionTracker.com. If you're running a mail server for your company on OS X do yourself a big favor and check this out! I run CommuniGate with MPP and could not be happier. I use MailShell for anti-spam and Sophos for AV. These two really cut down on the junk.
If you don't want to pay for Sophos and MailShell then you can plugin open source for filtering. I used ClamAV and SpamAssassin for a long time before I needed more options. (ClamAV can not clean a virus so mail with legitimate attachments gets rejected. With Sophos I can clean the virus from the message -- usually Word macro viruses -- and still deliver the mail.)
The support is also top notch. I swear these guys never sleep.
This review was originally posted on VersionTracker.com. If you need an anti-virus gateway to pass messages to Sophos, ClamAV or even other scanners, or to run past Spam Assassin, MPP is fantastic. I'm using it with Communigate Pro/Sophos/ClamAV, although it works witih Postfix and other mail servers. Very flexible, very stable. No speed hit, either. Highly recommended.