The problem there is there will be no pop3 requests. I'm only dealing with incomming smtp.
INTERNET --<smtp>----> Email appiance---<smtp>---> Exchange server--<propietary> -----> clients
And out going would bypass the appliance all together
Baracuda networks sells a similar appliance, but their reseller program is rather bad.
Thanks for the info on the virus scanner, that might help.