According to Rod Lasky from SmarterTools, there is no way to whitelist specific domains for ClamAV from within SmarterMail OR from within Clam as far as he could tell.
On the bright side, in SM 15 the Resend action does work, so if anything gets caught in the virus quarantine by accident, you can at least resend it, and it'll actually get where it's supposed to go.
Scott Hendrickson
SOS4Net, Inc.
Centennial, CO. U.S.A.