Rated 5 out of 5 stars

Very nice tools.
Please update for last release of thunderbird :)

This review is for a previous version of the add-on (3.0.0). 

I just released a new version 4.0.0 that should work in TB 78. It is currently still in review here on ATN, but you can already get it from https://github.com/lieser/X-Unsent_support/releases.