Brilliant! Rated 5 out of 5 stars
I tried the original "Remove Duplicate Messages" add on to attempt to remove about 2 thousand duplicates in a large IMAP folder after a mail migration. A horrible experience when it actually started creating multiple emails in the trash IMAP folder - 48 thousand of them until I had to forcibly kill TBird!!
Installed this alternate one and it had many more features, and quite simply just worked! Excellent - thank you so much!
I did get a "script has stopped responding" error which I just clicked continue through, but no complaints from me.