Lately I have problems deleting messages in Apple Mail (Mac OS 10.11). I select one or multiple messages, hit delete key and get an error saying that these messages have already been "deleted" (moved to the trash folder in Mail): that's not true, the trash folder is empty and I'm stuck with the problem.
What should I do? I tried also to rebuilt Mail's mailbox with Onyx utility, but the problem persist.
Any idea? Thanks