#10 - Letter Box
Letter Box :
1. a slot in a wall or door through which incoming post [DM] is delivered (US: mail slot, mailbox)
2. (less common) a box in the street for receiving outgoing letters and other mail (more usually called a postbox or pillar box) (US: mailbox)
See also Letterbox (US & UK): a film display format taking its name from the shape of a letter-box slot
