Rated 5 out of 5 stars

It is simple and does what you expect it to do. Maintainer was also very quick in helping with issues. For me it is a must-have add-on for thunderbird. (Note: It only works under some conditions related to the SMTP server and email headers - this is not the add-on's fault but a matter of typical constraints imposed by SMTP servers).

This review is for a previous version of the add-on (1.45).