Everytime I’ve installed avast this option “bat” appeared to choose but I never did. Question: What is this bat, afterall?
Most likely it is the outlook/exchange provider. It will stay “standby” until you actually open Outlook/Express as has been explained many times here.
Bat is probably, “The Bat”, an email program and, with the same name, an avast plugin for scanning messages into The Bat.
http://www.ritlabs.com/