ClamAV for Exchange Anti-Virus

Wouldn’t it be great if there were a free anti-virus package that could scan Exchange mail?  Normally anti-virus packages for Exchange are priced based on the number of Exchange mailboxes that will be protected.  In many cases, the cost to provide anti-virus protection for an enterprise can rise into the tens of thousands of dollars.  Well, maybe this isn’t needed: ClamAV, qmail and Exchange mail transport rules to the rescue!

Here is a diagram of a typical enterprise mailflow (grossly oversimplified):

Inbound filtering is generally performed to protect our users from SPAM and viruses.  Outbound filtering is sometimes not performed at all, but should be considered to protect our institution’s reputation (aids in staying off the RBLs).  Scanning within the Internal Exchange Environment is performed primarily to prevent a virus from spreading through our internal network.

So, the question becomes:  we know that we can configure Exchange to relay all mail destined for an external recipient through a smarthost, but can we convince Exchange that mail to internal recipients needs to be send through a smarthost too (but only once)?

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