Click on the Avast icon on your tray and when Avast opens, double click on the outlook e-mail provider. I think it is on the second and third tab marked smtp and pop3. There is a check box below that says "insert message into clean uninfected mail" or something close to that. You can have Avast insert a message into incoming mail and also outgoing mail that will show that Avast scanned it as "clean" with the vdf version that was used.
Hope that helps.