Rated 5 out of 5 stars

Try this if it didn't work :
(1) From Menu Bar, choose Tools / Add-on Options / Remove Duplicate Messages
*** If your Menu Bar is hidden, click on the Three Lines Icon on the right side of the Search Bar, then choose Customize and check the Menu Bar
(2) Go to Message Comparison tab, and try to change the elements used as the comparison criteria, and then click OK
*** In my case, I unchecked the Size element
(3) Run the Remove Duplicate action

Rated 5 out of 5 stars

I need a duplicate remover for a special folders (sent, ...)
Thank You!

Rated 3 out of 5 stars

Não está funcionando em pastas locais POP3.. mensagem chega sempre com tamanho diferente em 0,1 KB. Por exemplo: 29,6 KB e 29,7 KB na mesma mensagem. A mensagem é duplicada em todos os campos mas não encontra devido a diferença de tamanho em 0,1KB.

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

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). 

Rated 1 out of 5 stars

degrade form Remove Duplicates, this add-on cannot work on 78.4.0 (64bit) in my environment

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

Rated 1 out of 5 stars

Sorry, but I only get "No duplicates found" dialog box when I can see there are duplicates.

Thunderbird 68.12.1 on Windows 10 2004 x64

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

Rated 5 out of 5 stars

Message for TB - You HAVE to make the Extensions User interface less confusing and more easily navigable! Because your developers think "well WE know our way around it so we think it's fine" does NOT mean it's fine.
Where do I find the Config page for any particular Add-on (besides trawling the Web)?
As for RDM - It's not finding about 80% of my duplicates. I understand I have to find and tweak the Config page, wherever it is. (I used the previous one fine before having to un/reinstall TB and losing it.)
If/when I get it working properly I'll update here and add a *.
UPDATE - WHY does TB put specific Add-On settings in a completely different menu to the actual Add-On?!? Put this (also) in the Settings option ON THE PAGE FOR THE SPECIFIC ADD-ON! (FYI, they're in the main Menu: Tools: Add-on Options). Now it's done I'm upping to 5*, but I still want to know how to prioritise a Flag ("Replied") as the version(s) to Keep?

This review is for a previous version of the add-on (0.5).  This user has 2 previous reviews of this add-on.

Rated 1 out of 5 stars

Version 0.5rc1 does't work with TB 68.12.0
Version 0.4.1 works fine

This review is for a previous version of the add-on (0.5rc1). 

Rated 2 out of 5 stars

Xubuntu 20.04
Thunderbird 68.10.0
Remove Duplicate Messages 0.5rc1

1) I cannot see addon`s options window - any way.
2) Addon freeze on folder with 600 000 messages.

This review is for a previous version of the add-on (0.5rc1).  This user has 2 previous reviews of this add-on.

Rated 4 out of 5 stars

Beautiful extension, but in Thunderbird 78.2.0 (Italian version) I have a problem : when I activate the plugin it adds a button on the message bar.
If I remove the button, the button reappears the next time Thunderbird is restarted

This review is for a previous version of the add-on (0.5b3). 

Rated 5 out of 5 stars

This works perfect.

This review is for a previous version of the add-on (0.5b3). 

Rated 5 out of 5 stars

This was always one of the most useful Add-ons, and I'm glad it's been updated for 78.1.1, where it works perfectly. I can't praise it enough, and kudos to the author for his work on it.

This review is for a previous version of the add-on (0.5b2). 

Rated 1 out of 5 stars

Just run installation of this extension from source web site, and it immediately got blocked by McAfee antivirus program.

This review is for a previous version of the add-on (0.5b2). 

Rated 4 out of 5 stars

Latest version does not work with TB 68.11.0, no problems with 0.4.1

This review is for a previous version of the add-on (0.5b2). 

Rated 5 out of 5 stars

Works perfectly in Thunderbird 78.1.1 (64-bit). It's a great time saver and easy to use once you know where to set the options. There are so many criteria to choose from that makes this tool invaluable. I'm ecstatic that it has been updated so soon.

This review is for a previous version of the add-on (0.5b2). 

Rated 1 out of 5 stars

Does not work at all in TBird 68.11.0 (64 bit OSX). I selected the folder, right clicked and chose "Remove Duplicates". It is not that easy at all. I get the error "Not searching special folders" no matter what folder I choose. Don't know why people infer that others are dummies and it should work easily for everybody, like it did for them.

This review is for a previous version of the add-on (0.4.1). 

Rated 5 out of 5 stars

Works fine in TBird 68.10.0. Just select the folder, right click, and choose "Remove Duplicates". Doesn't get any easier. Don't know why people are having problems.

This review is for a previous version of the add-on (0.4.1). 

Rated 1 out of 5 stars

As BobBriscoe wrote, this modules does not work now for me.

This review is for a previous version of the add-on (0.4.1). 

Rated 2 out of 5 stars

So many reviews say they cannot work out how to use this addon because there's no documentation and it's not obvious. Me too. So, please, can someone who is using this successfully just spend a few minutes telling us how to use it? Surely that would make most of the (sometimes ungrateful) criticism go away.

One time, it worked for me (on Ubuntu 20.04 with TB 68.8.0). But only after I had found the config menu and deselected 'size' as a comparison criterion (having found this tip on the web). And only after I had given up then later found the output window in workspace #1 (I had launched the add-on from workspace #3).

But now, it seems to produce no output at all (I keep checking in all my workspaces). Does that mean that there's no duplicates, or that it isn't working? Please try to document this for someone who doesn't know what is meant to happen because they have never used it before.

Like others, I don't know the significance of the menu "Set original message folder(s) for next duplicate search". I suspect I'm meant to use this to select one folder, then right click on 'Remove Duplicates...' in any other folder (or the same folder). But, given the addon no longer gives me any output, I cannot test this theory.

The one time it worked, it was fast and useful...

This review is for a previous version of the add-on (0.4.1). 

Rated 4 out of 5 stars

Excellent outil, puissant et rapide.
S'il ne trouve pas de double, pensez alors a réparer le dossier (propriétés) pour mettre à jour le fichier d'index .msf et redémarrez thunderbird.
En 2 secondes il m'a trouvé 69 doubles sur un dossier contenant 49000 mails.

This review is for a previous version of the add-on (0.4.1).