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