Whether you're replacing an existing mailbox or installing a new one, you need to follow U.S. Postal Service requirements and regulations. Among these regulations is the mailbox height, which has been set with the carrier's safety and ease of delivery in mind.
Curbside mailboxes are typically mounted on 4-by-4-inch wood posts or 2-inch diameter metal poles. These posts or poles must be set into the ground so that when the mailbox is attached, the inside floor of the box is 41 to 45 inches above the ground. If you live in a residential area and your mail is hand-delivered, a mailbox can be attached to your house, but it must be easily accessible and 48 inches above the sidewalk, porch or ground.