Version:            (using KDE KDE 3.5.6)
Installed from:    Ubuntu Packages

First, thank you for adding this extremely usefull feature. I gave Evolution a try and in the migration I ended up with many duplications, in some cases up to 7 copies (if you multiply that to 16000 sent-email, you get the picture of the problem). I went back to KMail (after a really prolonged use of Evolution, which says something good about KMail) and the "remove duplicates" really solved much of the problem. Thank you!

Now, I have some ideas to improve it:

1- Be able to compare only some parts of the email, and by that I mean, from, to, cc, bcc, subject, and body. I've had 16000 sent-mail, now I have 26000, which is better than 40000 but there's a lot of duplicate there anyway. A close inspection in many of the emails showed me that the only difference is one field, like X-Status, or X-Evolution, or similar. I really don't care about maintaining separate messages because the X-Status is different while all the rest is the same. I think the remove duplicate feature should be configurable regarding what is compared and what is not, but this configuration should be hidden from the normal user (in some "advanced" tab) and some sane defaults be picked. What is sane is up to you, you know more about mail than I, maybe comparing all is the sane default.

2- Comparing duplicate messages in different folders. It happened to me that over time I've changed the way I ordered my email, so I know I have duplicates in various folders. It'd be nice to be able to find duplicates in folder X and all it's subfolders. Obviously, which one to delete? I think that a nice dialog should be shown here with the subject and both folders with the options to:
  - Leave both.
  - Delete one.
  - Delete the other.
  - Delete both.

3- Progress. This feature may be a must for feature 2. It'd be nice if you showed a progress dialago showing some kind of progress. It doesn't have to be exact or linear. A list with the delete messages would be nice. For ideas I'd recommend you to take a look at one of the plug ins for Gwenview or KPhotoAlbum that allows to remove duplicate images; a problem a bit harder that the email-one.

Thank you!