Empty Auction House Mail Bug

My boyfriend and I have decided to go Alliance. When he bought his transfer, it would not let him due to him having mail. The mail is already opened from Auction House. It is for an item that expired. It gave back the item, but the empty mail is just sat there now.

It wont allow him to delete it “This mail cannot be deleted”. Tried a few addons hoping they would help, as well as disabling all addons. Nothing is letting him delete this mail and ticket wait times are for days. Has anyone had this problem and found a solution?