Our site has been edicted to Microsoft Exchange server with a Barracuda 
spam filter.  There are numerous difficulties, one of which is spam not 
being filtered and non-spam being so filtered (significant increase in 
mission critical false positives).  At present, the administrative 
authorities (all of whom appear to be management professionals, not 
internals nor systems folks) insist on Exchange, allowing open systems 
standards compliant end-users to have IMAP service.  Given this, what 
are the best server-side spam filters, either hardware or software?  
"Best" should be based upon current field-deployed experience and/or 
unsolicited external reviews (not vendor-supported "independent" reviews).

Thanks for any information.

Yasha Karant