Rated 5 out of 5 stars

It worked perfectly for me. I believe the people that it isn't working for haven't set the search properties correctly on the add-on. If the message has ever been moved on the source end, then the message ID will be different and not seen as a duplicate. Just uncheck message ID and check date& time, sender, receiver, subject, and body are the same, and check save the first message.

This review is for a previous version of the add-on (0.5.2.2).