Review for Remove Duplicate Messages by Malcolm
Rated 5 out of 5 stars
This worked very well for me, Thunderbird 78.8.0 on Windows 10. I did have to tweak the settings a bit following the advice in the other reviews. I found it surprisingly fast finding the dupes.
This review is for a previous version of the add-on (0.5.1b2).To create your own collections, you must have a Mozilla Add-ons account.