Rated 4 out of 5 stars

After some experimentation, resolved the problem I experienced in my previous review. And as a result, upped the rating to 4/5 stars. Not 5 stars as that problem and its work-around are not obvious.

The problem is that when you first install the addon and try to use it (either before or after restarting Thunderbird 17.0.x), it does not detect POP account "Trash" folders properly.In the Duplicate Messages Deletion window that appears after detecting dups, at the bottom are the choices "Delete permanently" and "Move to...(drop down list of folder choices)". "Move to..." defaults to "Trash". But leaving that choice alone, it will not properly detect the Trash folder on the account you are detecting dups on, unfortunately. Which means dup messages get permanently deleted, even if you don't want them to be.

To avoid this problem, you first have to open the drop down list beside "Move to..." and manually select the Trash folder for the account you are detecting dups on. Then and only then will your dup messages get properly sent to Trash. In the future it will remain properly selected, so you only have to do it once. Don't know if you have to manually change it for every account you are working on, but I do so to be safe.

This is still a problem and still needs fixing, but at least there is a way around it until its fixed.

EDIT: replying to the author response below. Thanks for the response, but unfortunately you totally misunderstand what the problem is. I elaborated more in my original review linked to at the bottom of this post; might want to look at it.

The problem has _nothing_ to do with "detecting duplicates in trash". The problem is when detecting duplicates in the INBOX of a selected account, the "Move To..." selection defaults to "Trash" (of that account). And by default, it doesn't actually move your messages to there as you would expect. It instead wrongly permanently deletes them.

To work around this problem, you must manually select the "Move To..." folder (Trash or otherwise) for each account in the drop down list.

If you don't do that and instead rely on the default "Move To...Trash" location without adjusting anything manually, your mail gets permanently deleted out of the Inbox when you didn't want it to after pressing "OK". That's the problem.

This review is for a previous version of the add-on (0.3.7).  This user has a previous review of this add-on.

Practically all users expect Trash folders to be skipped when looking for duplicates. This is both because dupes are usually deleted to the trash (incl. manual deletion), and because, more generally, whatever's in the trash is already not really part of your mailbox, it's deleted-but-undisposed-of. So, it would certainly not be a good idea to change this default behavior.

I understand you might like/expect something different, but you must recognize you're in the minority. For you (and others), there's the preferences dialog with which you can change such settings.