From Longman Dictionary of Contemporary Englishoutboxout‧box, out box /ˈaʊtbɒks $ -bɑːks/ noun [countable] 1 the place in a computer email program where messages that you have not sent yet are stored → inbox2 American English a container on an office desk that is used to hold letters, documents etc that have been dealt with and are ready to be taken away by someone such as a secretary SYN out tray British EnglishFrom Longman Business Dictionaryoutboxout‧box /ˈaʊtbɒks-bɑːks/ noun [countable]1COMPUTING the place on a computer where email messages that you have not sent yet are stored2American EnglishOFFICE a flat container used to hold letters, papers etc that have been dealt with and are ready to be taken awaySYNout-tray BrE → compare inbox
