@Karsten
I too can delete e-mails and some do delete as expected, but if I have a list of 10 e-mails and delete them one-by-one, not all will move to the Deleted Items folder. The deleted items folder updates with the correct number of items, but those items that did not delete correctly "remain" in the Inbox.
When you were able to delete these, what was a timely manner? If I delete e-mails straight after each other, I end up with problems as before. Some e-mails delete, and some remain and subsequent attempted deletes or moves result in "Unknown Error" or "Can't move this item".
I am not aware of the public folder issues, and I will attempt to test this on my systems.
Can anyone else shed some light on this (successful or not)?