This one I call: The "Mailbox".
Which also comes with a way to tell if you've got mail.
Typing 'Mailbox' instead of 'Postbox' reminds me of a scene from my time working in the US.
ME: (TO DEPARTMENT SECRETARY & OTHERS NEAR HER DESK) Where can I post a letter around here?
SECRETARY & OTHERS: (BLANK LOOKS)
ME: I've got some post to send.
SEC & OTHERS: (STILL BLANK, UNCERTAIN)
ME: (SHOWING LETTER) Where do I take this?
SEC & OTHERS: (BRIGHTENING) Oh. The Post Office.