While the typical rural mailbox works well for suburban neighborhoods, it falls short in meeting the burgeoning needs of city life. As skyscraper condos, apartment buildings, and multi−floor office buildings grew taller, a demand for mailboxes in limited spaces emerged. Thus, mailbox design experts, following the strict guidelines of the United States Postal Service (USPS), began to cluster mailboxes together for the collection and distribution of mail in multi−family residences and tall office buildings.
These wall−mounted horizontal and vertical mailboxes provided a secure way for city dwellers and office workers to receive their daily mail. To provide city planners, architects, building superintendents, and contractors with appropriate standards for wall−mounted commercial mailboxes, these mailboxes were rated. Earlier versions of the vertical mailbox and horizontal mailbox types were rated STD−4B, which meant the mailbox conformed to specific form factors and mailbox security levels.
Later, specifications were altered to increase the security of wall−mounted vertical apartment mailboxes and wall−mounted horizontal apartment mailboxes (also referred to as cluster mailboxes or CBU mailboxes). The newer rating for apartment mailboxes was entitled STD−4B+ to indicate the increased security of these commercial apartment mailboxes.
Eventually, thirty years later, in 2004, the USPS again increased the mailbox security requirements of apartment wall−mounted mailboxes and rated all new commercial mailboxes that met this level of security as STD−4C (which replaced all previous regulations for wall−mounted commercial mailboxes).
The STD−4C regulation stands for Standard−4C and became effective on October 5, 2006 for any commercial or apartment wall−mounted mailbox that is a part of new construction or major renovation. The STD−4C commercial mailbox rules, which govern both design layout and installation, are the same regardless of whether the cluster mailbox unit (CBU mailbox) is installed outdoors or indoors. Thus, this regulation applies to any centralized, wall−mounted mailbox located either in an office or apartment building or office high−rise or even within a single−family suburban subdivision as an outdoor centralized mailbox kiosk.
A major distinguishing feature of the 4C mailboxes is their much larger size. Designed to accommodate today’s mail size, these 4C mailbox units require about three times the space of any previous wall−mounted cluster mailbox units. Manufacturers refer to the new 4C mailboxes and cluster box units as centralized mail delivery equipment which may be any type of clustered mailbox including pedestal−mounted cluster mailbox units (CBU), free−standing mailbox units, cluster mailbox kiosks, cluster mailbox shelters, or other wall−mounted cluster mailboxes.
Of course, this regulation did not affect STD−4B commercial boxes and STD−4B+ commercial boxes but manufacturers of those units did provide upgrade kits for these mailbox installations in order to enhance the security of these commercial apartment mailbox units. These STD−4B and STD−4B+ security upgrade kits harden the arrow lock master door (which typically was the most vulnerable part of the older commercial boxes).