Cannot transfer server because of mail in mail box but noting in my mailbox
Make sure you don’t have mail from players you’ve ignored. It won’t show in the mailbox, because of the ignore status, but it would still be there blocking the transfer.
Also, if you’ve done some quests in the last 24 hours, the NPCs involved may send you mail that are en-route and would block transfer even if you aren’t expecting them. In my limited observation, it’s best to completely leave a character alone for 48-72 hours before requesting transfer (after making one last check of the mailbox), so you don’t do something that will create inbound mail from the system.