- a public box in which mail is placed for pickup and delivery by the post office.
- a private box, as at a home, into which mail is delivered by the mail carrier.
- a file for storing electronic mail.
- mainly US and Canadian
- a slot, usually covered with a hinged flap, through which letters, etc are delivered to a building
- a private box into which letters, etc, are delivered
- a public box into which letters, etc, are put for collection and delivery
- (on a computer) the directory in which e-mail messages are stored; also used of the icon that can be clicked to provide access to e-mails
