NCN InterNetworks BV has the solution for you, realtime virusscan.
What it does, it scans for virusses and trojans when the mail is delivered to your mailbox.
If theres a problem with it, the mail will be put in quarantaine. You decide if you want the mail in question or not. With this solution you are protected from virusses before they can even reach you, right here at NCN HQ.