My Comcast email is delivered via ports 110 (POP) and 25 (SMTP) and is scanned by avast. However Comcast does also offer secured ports for POP/SMTP so just check the ports you are using in OE and Windows live mail.
If you are connected directly to the Comcast network then there is really no concern about using the unsecured ports 110 and 25. If you connect to get your Comcast mail from other locations like cafes, airports, hotels then you will need to use the secured connections and use the free product STunnel to manage the secure connections and still allow avast to scan the mail.
If you can wait a bit longer then avast have said that the management of the secure email connections (allowing avast to scan the mail delivered via them) will be provided directly in the next major release of avast (avast 5).