I am running Mozilla mail, version 1.6, off of which Thunderbird is built. Right click on account name, go to Server settings:
Server name should be 127.0.0.1
User name should be your account name, for instance,
denro@anISP.net#myISPpopserver
Then go to Outgoing Server (SMTP) and do similarly with Server name and user name. This works well and i have tested with with eicor.com in a zip file both sending and receiving and avast scans the email IMO better than Norton.
Hope this helps