Front Loading (FL) Horizontals: please note that one door will be used as either a postal door (for U.S. Postal approved units) or as a master door (for private access units), and cannot be used as a tenant door. However this door can be used as an outgoing mail slot or as an office drop box upon request, but ONLY on private use/access units. Each compartment measures 15" deep. Other (custom) larger door sizes and configurations are available upon request. These mailboxes are wall mount recessed style units. Recommended minimum wall opening depth is 17".