We're using MailScanner as our mail gateway and found it excellent. Our 
setup is FreeBSD 5.3 + sendmail + SpamAssassin + ClamAV + BitDefender + 
F-prot. MailScanner can also work with Linux and Postfix/Exim too. The 
link is http://www.sng.ecs.soton.ac.uk/mailscanner/

Another one, purely for gateway (also based on MailScanner), is 
SMGateway from http://www.fsl.com/products/fsmg.html The package only 
work on RedHat Ent or CentOS but added many features.

Both are free to use. You can pay SMGateway for support.

Cheers
Raylund

Chris Bagnall wrote:

>>   The author is implying something be developed with m0n0 
>>simplicity and reliability for the task of spam filtering.  I 
>>personally think it is an excellent idea since spam filtering 
>>is a nightmare to set up.
>>    
>>
>
>You might want to look at ART's Project Gamera:
>
>http://www.atomicrocketturtle.com/modules.php?op=modload&name=Sections&file=
>index&req=viewarticle&artid=20&page=1
>
>I've not used it personally, but I have used quite a few of his packages on
>webservers running the Plesk control panel, and they've enhanced
>functionality considerably.
>
>FWIW, if you are looking for a mail filtering system, you can't go too far
>wrong with Postfix + SpamAssassin + ClamAV.
>
>Regards,
>
>Chris
>  
>