Hello Ladyhawk, welcome to the forum.
There is a specific email provider (or module) included with Avast. It is designed to scan email arriving via an email client, such as Thunderbird or Outlook Express. Mail in a Gmail or Incredimail account, if accessed through the browser rather than an email client will be scanned by the webshield and the standard shield. (Unless the connection is https, in which case it will only be scanned upon opening,
I think.)
If you left click the tray icon, the resulting window contains information concerning all providers installed during installation of the program. The maximum number is 7. They are: Standard, Web Shield, Network Shield, Email, Outlook/exchange, and P2P.
If any of the programs the shield is designed to protect is not running, the provider will have the message "the provider is waiting for a sub-system to start." (If you never use that sub-system, the provider can be terminated.)
If you removed AVG correctly and used the
removal tool Avast should work correctly.
If you have the remnant of almost any other AV still on the computer (example Norton or McAfee) it is likely there would be a conflict, and the appropriate removal tool should be run.