Choosing Centralized Mailboxes that Comply with the US Postal Service Regulations


All new construction and major renovation projects require U.S. Postal Service STD-4C compliant mailbox systems as of October 5, 2006. The USPS 4C Standard for wall mounted mailboxes includes the following specifications:
  • New compartment form factor minimum size requirement of 12″W × 15″D × 3″H
  • Eliminates the vertical form factor (5″W × 6″D × 15″H) design
  • Introduces parcel locker requirement based on a 1:10 ratio of parcel lockers to customer compartments (there must be a minimum of 1 Parcel Locker for every 10 Tenant Compartments)
  • Strengthens security requirements for the entire receptacle
  • Standardizes and improves tenant compartment lock design
  • Meets Americans with Disabilities Act (ADA) standards

4C Horizontal Wall Mount High Security Mailboxes from National Mailboxes are designed to meet or exceed the USPS specifications outlined above and in the Federal Register/Vol. 69, No. 171/September 3, 2004/Rules and Regulations POSTAL SERVICE, 39 CFR Part 111, Standards Governing the Design of Wall Mounted Centralized Mail Receptacles.


These three simple questions below will help you determine if you need to use 4C Horizontal Wall Mount High Security Mailboxes from National Mailboxes for your next centralized mail station:

1. Are the mailboxes being used in new construction?

2. If renovating, are mailboxes simply being replaced using the same rough opening (RO)?

  • If Yes then 4B+ rated verticals or horizontals may be used
  • If No then STD-4C MUST be used
  • If adjusting RO or adding new mailboxes then new 4C rated mailboxes MUST be used

3. Is the mailbox installation inside or outside?

  • If inside, choose mailboxes based on answers to Question 2
  • If outside and “unprotected” then 4C or CBU products MUST be used


  • A “major renovation” would occur anytime the condition of the wall where the existing wall mounted mailboxes are presently installed is being modified.
  • If the cavity of the wall is altered in such a manner the mailboxes can’t be reinstalled on a one-for-one basis, 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 will be applied to a specific project, please contact your local Postmaster or Postal Delivery Planning Official for guidance prior to purchasing any wall mounted mailbox systems.

ADA Compliance

The USPS 4C Standard includes a requirement to meet Americans with Disabilities Act (ADA) standards. The ADA section that covers clear space and reach dimensions is noted below and can be found in the ADA Accessibility Guidelines for Buildings and Facilities Appendix A to Part 36 – Standard for Accessible Design Section 4.2 Space Allowance and Reach Ranges

4C Units shall be designed such that they are in compliance with the following installation requirements:

  • At least one customer compartment shall be positioned less than 48 inches from the finished floor
  • No parcel locker compartment (interior bottom shelf) shall be positioned less than 15 inches from the finished floor
  • No tenant lock shall be located more than 67 inches above the finished floor
  • No customer compartment (interior bottom shelf) shall be positioned less than 28 inches above the finished floor
  • The USPS Arrow lock shall be located between 36 and 48 inches above the finished floor


Additional Information:

4C Horizontal Mailboxes – USPS Approved and STD-4C Compliant
Accessibility Installation References and ADA Requirements
Shop all Commercial Mailboxes from National Mailboxes