mail slot
noun [ C ] US uk/ˈmeɪl ˌslɒt/ us/ˈmeɪl ˌslɑːt/ (UK letterbox)
（房屋或其他建筑物入口处的门或墙上的）信箱
a rectangular hole in the door or in a wall near the entrance of a house or other building, through which letters, etc. are put
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