letterbox

剑桥词典

(US mail slot)
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
投递口，投信口
(US mailbox)
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
邮政信箱，信筒 返回 letterbox