If it is retrieved using the pop3 protocol probably, if the email arrives in the inbox like normal email. If it did scan it you would be able to see the Scanned Count and Last Scanned data change in the Internet Mail provider and see avast antivirus information in the email headers.
However, I suspect that it doesn't use pop3 protocol but something like OE does when it imports/converts hotmail and that pulled then into a separate folder.
Unfortunately, I don't use either product to be more helpful.
