Rated 4 out of 5 stars

A great addition to Thunderbird and a worthwhile update with respect to the standard spell checker on my pc.
By default, your spelling is checked remotely, but a locally hosted version is available if you are worried about your privacy. If the setup process of the local host implementation were easier, it would get 5 stars from me.

This review is for a previous version of the add-on (4.2.12).