Does such a plugin exist?
I am using Avast Free 5.0.677
The one available from RITLabs, the maker of The Bat, at http://www.ritlabs.com/en/products/thebat/plugin/plugins.php does not work. In the bat configuration it shows an error. See attached below:
I’m afraid that plugin was for avast! 4.x only.
However, the Email Shield in avast! should work just fine, i.e. there shouldn’t be any need for a special Bat plugin.
Good to know igor. 
@ garmshop, is The_Bat email working without the plug-in for you?