The 450 series horizontal mailboxes were designed for use in large private institutions not serviced by the USPS such as military bases, colleges, universities, and hotels. These heavy-gauge front loading aluminum locking mailboxes meet all USPS regulations except those pertaining to compartment size. The smaller compartments allow more mailboxes per module, and are useful in areas with limited wall space. Each door of this secure mail system features a 5-pin cam lock with two keys and a clear plastic window number slot for tenant identification. Please note that one door will be used as a master door and cannot be used as a tenant door, but can be used as an outgoing mail slot or office dropbox, upon request.