Rated 5 out of 5 stars

This is an extension where it pays off to read the documentation first, I especially recommend the FAQ on the GitHub wiki. Once you understand how to use it, it's just awesome! The default criteria for identifying duplicates are, sensibly so, very strict, but you can easily adjust them if the extension doesn't find the duplicates for your particular case. In my case, the duplicates in the Sent folder had slightly different timestamps and message size, but once I set the extension to use minute precision and ignore message size, it found all of them. The preview window also makes it really easy to inspect the results. Using Thunderbird 78.5.0

This review is for a previous version of the add-on (0.5).