Briefeinwurfschlitz {m}; Briefeinwurf {m}; Briefschlitz {m} - letterbox [Br.]; letter slot [Br.]; mail slot [Am.]/mailslot [Am.]
Briefeinwurfschlitze {pl}; Briefeinwürfe {pl}; Briefschlitze {pl} - letterboxes; letter slots; mail slots/mailslots