STD-4C Mailboxes: How They Differ From the Old STD-4B Standard

The United States Postal Service (USPS) has been encouraging homeowners and business owners to use centralized mail delivery systems for decades.  The United States Postal Service (USPS) has long supported centralized mail delivery systems as a way to streamline operations and reduce costs. Since the introduction of residential curbside Cluster Box Units (CBUs) in 1967, centralized systems have become the gold standard for both residential and commercial developments. it is a form of centralized mail delivery, CBUs streamlined the delivery of mail by providing mail couriers with a single drop-off point for multiple residences. Since then, the USPS has released specifications for other forms of centralized mail delivery systems

Cluster Box Unit (CBU): A USPS-approved mailbox unit that consolidates mail delivery into a single, centralized location, typically serving multiple addresses in a community or development.

Over the decades, the USPS has developed specific engineering standards to guide mailbox design and compliance. The two most notable standards are STD-4B and the more recent STD-4C. Understanding the difference between these standards isn’t just academic—it can determine whether your development passes inspection, qualifies for mail service, and meets resident expectations for durability and aesthetics.

What Are STD-4B Mailboxes?

STD-4B mailboxes were introduced in the 1970s and were commonly used in multi-unit residential and commercial buildings. These units typically featured vertical compartments and were mounted in recessed wall spaces or as surface-mounted arrays.

Q: "Are 4B mailboxes still legal?" A: Only for pre-2006 buildings. USPS mandates that all new constructions must use STD-4C-compliant systems.

These mailboxes served well for decades, but their designs lacked modern security features, efficient package delivery capabilities, and accessibility accommodations.

STD-4B: An outdated USPS mailbox standard featuring vertical compartments. These are no longer compliant for new construction or major renovations.

What Are STD-4C Mailboxes?

Released in 2004, the STD-4C standard reflects a complete redesign in how centralized mail is delivered. These mailboxes feature horizontal compartments, built-in parcel lockers, ADA-compliant reach ranges, and enhanced security elements like internal hinges and tamper-proof locks.

By 2006, USPS began requiring all multi-unit buildings with permit applications dated on or after October 6, 2006 to use only STD-4C mailbox systems.

STD-4C: The current USPS mailbox standard that requires horizontal compartments, parcel lockers, and ADA-compliant design for all new multi-unit developments.

Can STD-4B Mailboxes Still Be Used?

Yes—but with significant limitations. STD-4B systems can only be installed in properties built before October 6, 2006, and only as a like-for-like replacement. If you're remodeling and changing mailbox configurations, the USPS will likely require a shift to STD-4C compliance.

Q: "Can I upgrade my old 4B system without switching to 4C?" A: Only if you're doing a direct replacement with no structural changes. Otherwise, 4C is mandatory.

Key Differences: STD-4B vs STD-4C Mailboxes

1. Construction and Durability

   • STD-4C units are built with heavier gauge steel and stronger internal hardware for maximum durability.

2. Tenant Compartment Size

   • STD-4C compartments are larger and more accessible, accommodating a wider variety of mail and packages.

3. Security Enhancements

   • Internal hinges, anti-pry doors, and USPS arrow locks make 4C significantly safer for residents.

4. Parcel Lockers Included

   • The 4C standard mandates 1 parcel locker per every 10 mailboxes, greatly improving package security and delivery efficiency.

Parcel Locker: A secure, oversized compartment used in cluster mailboxes to safely store resident packages for retrieval without requiring a signature.

5. ADA Compliance

   • Reach ranges and installation height for 4C are designed to meet the Americans with Disabilities Act (ADA) guidelines.

Why It Matters for HOAs, Developers, and Property Managers

Failing to follow USPS regulations on mail delivery systems can lead to:

• Delivery delays or refusals

• Costly retrofits

• Complaints from residents

• Potential legal risk for non-compliance

When planning new developments or renovations, choosing a compliant STD-4C mailbox system from the start isn’t just smart—it’s necessary.

Q: "Do CBUs come in STD-4C formats?" A: Yes. Most modern CBUs are fully compliant with STD-4C standards, including parcel lockers and ADA accessibility.

Make the Smart Mailbox Move—Now

Whether you're upgrading an older 4B system or planning a brand-new community development, don’t let outdated mail delivery undermine your project. Forsite Mailboxes and Signs provides turnkey STD-4C mailbox solutions, from planning and permitting guidance to delivery and installation.

✅ Fully USPS-compliant 4C mailbox units
✅ Custom-finish options to match community branding
✅ Integrated parcel lockers and accessibility features
✅ Expert guidance on regulations, layout, and installation

About Forsite:

Welcome to Forsite! You’ve found your best source custom street signs and community wayfinding signs. We manufacture and install upscale site amenities throughout the United States.

Forsite can provide all of your signage needs for your Master Planned Community or  Residential Development. We help our customers to create a uniform, upscale appearance and increase property values by "bundling" themed packages of decorative street signage, mailboxes, post and wall mounted lighting, and wayfinding signage

You can count on the experts at Forsite to help improve the quality of your community today. Contact us today to get started by talking to one of our experienced team members at 855-537-0200.