I believe that a way to notify users of why the staff deleted or rejected their posts could be a useful feature.
That would avoid having to open a private thread or emailing them manually.
It could be a notification or a popup like when a user gets suspended.
It could be sent via email too if the user has mail notifications enabled.
This shouldn't be mandatory and shouldn't be available for standard users deleting their own messages.
I didn't find similar suggestions, so I opened this thread.