letterbox
noun [ C ] UK uk/ˈlet.ə.bɒks/ us/ˈlet̬.ɚ.bɑːks/
(US mail slot)投递口，投信口
a rectangular hole in the door or in a wall near the entrance of a house or other building, through which letters, etc. are delivered
(US mailbox)邮政信箱，信筒
a metal container in the street or other public place in which you can put letters for them to be collected and sent to someone else