3 DOOR VERTICAL MAILBOX-ALUMINUM FINISH-SURFACE MOUNTED-USPS ACCESS Salsbury vertical 3500 series mailboxes have been approved to the required security upgrades of USPS-STD-4B+ and are ideal for apartments, condominiums, commercial buildings and many other applications. Surface mounted units mount directly to a wall or other flat surface and are secured with mounting hardware through the back panel. Custom engraved self-adhesive placards (related item #3567) are available as an option upon request. A 4-3/4'' W x 1/2'' H outgoing mail slot (related item #3569) is also available as an option upon request. It will be located in the far left door of the unit unless otherwise specified. If a mail slot is requested, order unit with one additional compartment than the total number of tenants receiving mail.