I had some mail duplication and on choosing to delete duplicates it worked partially. It delete all duplicates except one. I.e. for each mail that that more than one duplicate it delete those. But I still have two copies of each duplicated mail. This is different from Bug 340759 - deleting duplicate mails has no effect where I didn´t see an effect at all. But that was with local maildir folders. This one is with Exchange IMAP. But then it might be that its related still, as I am not sure whether I actually had mails in there duplicated more than once. Reproducible: Always Steps to Reproduce: 1. Select a folder. 2. Duplicate some mails several times 2. Choose "Folder/Delete duplicates" (don´t know the exact translation, as I use KMail with german localization) 3. Actual Results: All duplicates of one mail are deleted, except one, so that I have two mails for each duplicate mail, instead of one. Expected Results: One mail for each previously duplicated mail.
This bug has never been confirmed for a KDE PIM version that is based on KDE Frameworks (5.x). Those versions differ significantly from the old 4.x series. Therefore, I plan to close it in around two or three months. In the meantime, it is set to WAITINGFORINFO to give reporters the oportunity to check if it is still valid. As soon as someone confirms it for a recent version (at least 5.1, ideally even more recent), I'll gladly reopen it. Please understand that we lack the manpower to triage bugs reported for versions almost two years beyond their end of life.
Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.1 aka 15.12, preferably more recent), please open a new one unless it already exists. Thank you for all your input.