Rated 5 out of 5 stars

Thunderbird does'nt have this - goodbye thunderbird. It is the best, you have like me several addies. This will inform you of all, just let it know which you use. Installed 2 days ago and wondered how I did without it.
Robbie - use right click on toolbar - click customize. Then find & drop notifier.

This review is for a previous version of the add-on (2.3.1).