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How the U.S. Postal Service STD-4C Regulation Affects Centralized Mailbox Selection

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What is the "4C" Postal Standard?

The "4C" postal standard requires that 4C horizontal mailboxes and parcel lockers be installed in all new construction projects and major renovations effective October 2006.  The United States Postal Service addressed the shape of mailbox compartments and the demand for more secure mail and parcel delivery with new standard, USPS-STD-4C.  This standard replaces the traditional cube style compartments with more flat style compartments as well as incorporates fully integrated or stand-alone parcel locker options into the mailbox.  A minimum of one parcel locker is required for every five (5) tenant compartments (effective July 2020).  Parcel locker are not required in installation sites with less than five (5) tenant compartments.  Salsbury Industries 3700 Series 4C standard and custom high security horizontal mailboxes and fully integrated and stand-alone parcel lockers have been USPS approved and meet the specifications of USPS-STD-4C.


How Do the New Regulations Affect How I Buy Centralized Mailboxes?

The quesitons below will help you determine the right wall-mounted mailbox product for your project.
1. Are the mailboxes being used in new construction?
    a. Only "4C" rated wall-mounted mailboxes or free-standing Cluster Box Units (CBU's) can be used.
2. Are the mailboxes being replaced using the same rough opening (R.O.) for renovation?
    a. "4B+" rated horizontal mailboxes or vertical mailboxes can be used. Contact your local postmaster for details.
    b. If the rough opening will change, then new "4C" rated mailboxes must be used.


What Constitutes a "Major Renovation"?

A "major renovation" would occur anytime the condition of the wall is being modified where the existing wall-mounted mailboxes are presently installed.  If the rough opening of the wall is modified, the renovation would be considered "major" and mailboxes complying with the new USPS STD-4C regulation should be installed.
If you have any questions about which USPS mailbox standard should be applied to a specific project requiring "USPS Approved" mailboxes, please contact the local Post Office for assistance prior to purchasing your mailboxes.