The 500 Series front-loading horizontal mailboxes are designed for use in larger multi-family apartment buildings, dormitories, office buildings, and more. These high-security mailbox units can accommodate either U.S. Postal Service or private party access. The included lock type is a 5-pin tumbler lock with 1,000 key changes, two keys, and a clear plastic name/number slot for identification by tenants.Please note that one door must be used as either a postal door (for USPS approved units) or 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.