Hello 
As a user with no staff privileges its is very difficult to tidy up your inbox as there is no icon for bulk actions. At present, this option is available for staff as seen in this image below but not for other users.
This means that if you want to archive a lot of personal messages you have to do this individually by entering the message and pressing Archive. This makes life rather difficult.
As such, my suggestion would be to include a bulk select menu for messages for non staff users with these options to make a bit easier. An example:
