Prior to USPS mailbox regulation changes in 2006, horizontal mailboxes were the standard for many large multifamily residential and business mail delivery applications. However, these time-tested mailboxes may now only be used in direct one-to-one replacements in facilities with U.S. Postal Service mail delivery. When initiating a replacement or renovation project - it is always a good idea to get the approval from your local postal authority before altering the mail system in your building; but in general, if your project is not disturbing the wall the mailboxes are already mounted in, then replacing old mailboxes with a product similar in style is typically acceptable. Any adjustment to the rough opening in the wall and all new construction will require new STD-4C compliant mailboxes.

Horizontal mailboxes are still an excellent mailbox solution for any private delivery installation such as university dorms, internal business office distribution, or a myriad of other private applications.