Rated 3 out of 5 stars
Thunderbird did a dirty trick when my profile was damaged and auto updated itself. Now I find most of my addons don't work, and this is one of them. I've used it for about 7 years or so and found it very useful. The ability to have custom alerts for different accounts and folders (useful when using server side filters) and the ability to silence the alert for routine mail such as newsletters etc was invaluable. I hope it can be updated or a replacement arrives soon.
The star review is simply because it doesn't work (can't give it full marks when it doesn't work!), otherwise, it would get full marks.