All incoming mail moved to trash

has anyone ever seen a problem whereby the server copy moves ALL incoming email into Trash ? I just found at 5:50am (when I was asleep!) that the server moved every single email I had received into trash, and the only email I could see was sent & saved email.

I was able to do a restore all from trash, but I’d be interested to know how this could happen. I have no special rules or agents in place. Obviously something happened at the server end.