letter-box
n
(a) (Brit) opening in a door, covered by a movable flap, through which letters are delivered 投信口.
(b) (US `mailbox) box near or at the entrance to or inside a building, in which letters and other articles brought by the postman are placed 信箱. =>illus at App 1 见附录1插图, page vi.
(c) = post-box box (post3).