The U.S. Postal Service (USPS) has very strict rules and regulations governing the ownership, style, installation and maintenance of mailboxes. The installation of mailboxes is permissible through an arrangement between the developer or homeowner and the local postmaster.
The homeowner is responsible for installing and maintaining curbside mailboxes to USPS specifications. If you plan to replace an existing mailbox, check with the Postmaster if you wish to change the location or construct a custom box.
For cluster mailboxes, the builder is responsible for installing a concrete pad according to USPS specifications and the local postmaster provides the cluster boxes, their installation and maintenance.
Most information is available through the U.S. Postal Service's website at https://www.usps.com/.