A post box, also known as a collection box, mailbox, letter box or drop box, is a physical box into which members of the public can deposit outgoing mail intended for collection by the agents of a country's postal service. The term post box can also refer to a private letter box for incoming mail.

A letter box, letterbox, letter plate, letter hole, mail slot or mailbox is a receptacle for receiving incoming mail at a private residence or business. For outgoing mail, post boxes are often used for depositing the mail for collection, although some letter boxes are also capable of holding outgoing mail for a carrier to pick up. Letterboxes or mailboxes use the following primary designs:A slot in a wall or door through which mail is delivered A box attached directly to the building A box mounted at or near the street A centralised mail delivery station consisting of individual mailboxes for an entire building also known as a "flock" throughout the South Island of New Zealand and parts of America. A centralised mail delivery station consisting of individual mailboxes for multiple recipients at multiple addresses in a particular neighborhood or community