Review for Remove Duplicate Messages by John Elliott
Rated 5 out of 5 stars
My laptop was accidentally destroyed and I had to rebuild my email from various backups and copies stored on other machines.
The plugin was absoluetly brilliant - there was one bug (which I manged to work around) but I let Eyal know and he fixed in a matter of days.
To create your own collections, you must have a Mozilla Add-ons account.