From your screenshot, I would assume that it was added after the fact.
It is oddly listed in all caps, which is not the norm for a mailbox. I also noticed that AOL (shudder, :black: ) is showing at the top of your mailbox window, it could be possible that any software that you installed for AOL might have added it. If that is the case, you would want to check with AOL support to see if that feature is available.