From Longman Business Dictionary
inboxin·box /ˈɪnbɒks-bɑːks/ noun [countableC]1COMPUTING the place on a computer where new email messages arriveAn email filter will stop your inbox from filling up with spam.
2American EnglishAmEOFFICE a flat container used to hold letters, papers etc that need to be dealt withSYN BrE in-tray → compare outbox