STD-4B vs. STD-4C Mailbox Systems: What to Know in 2025

If you’re a developer or property manager planning centralized mail delivery, you’ve likely come across the acronyms STD-4B and STD-4C. These aren’t just technical terms—they’re regulatory distinctions that carry big implications for compliance, usability, and your bottom line.

Understanding the differences between 4B and 4C mailbox systems is essential for making the right decision for your next installation. And with USPS regulations evolving, making the wrong call could result in installation headaches or failed inspections.

STD-4C: The current USPS standard for centralized mail delivery systems in all new construction and major renovations. Designed for better security, accessibility, and mail handling.

1. What’s the Difference Between 4B and 4C?

STD-4B mailboxes were once common in older apartments and buildings. These vertical-style units are now considered outdated and non-compliant for new installations. STD-4C mailboxes, on the other hand, feature horizontal compartments, parcel lockers, and accessibility improvements—and are now required by the USPS for all new builds.

Q: Can I still use 4B mailboxes?
A: Only in limited retrofit cases. For any new construction or major remodels, USPS mandates the use of STD-4C mailboxes.

2. Why STD-4C Is the Better Long-Term Investment

Choosing a 4C system is not just about following the rules—it’s about future-proofing your property. 4C units include parcel lockers, better theft resistance, ADA-compliant reach ranges, and more efficient delivery setups. They also support growing package volumes, unlike older 4B systems that were never designed with Amazon in mind.

Parcel Locker: A dedicated, locking compartment built into a CBU or 4C mailbox system for securely storing resident packages.

3. Retrofit or Replace?

If you’re managing an older property with 4B boxes, you may be eligible for a USPS-approved retrofit—but be careful. If the remodel is considered substantial (especially if wall cavities are altered), you may be required to upgrade to 4C.

We always recommend planning with future compliance in mind. Installing 4C now ensures you're not forced into expensive upgrades later.

4. Configurations and Customization

4C mailbox systems come in versatile configurations—standalone units, wall-mounted setups, or even kiosk-style designs. Whether you’re outfitting a lobby, community center, or new housing development, there’s a compliant option that fits.

Still Unsure What’s Right for Your Site?

Not sure what your site requires—or whether your remodel qualifies for a 4C upgrade?

Forsite has helped hundreds of property managers and developers navigate USPS requirements with confidence. From layout guidance to final delivery, we’ll make sure you’re on the right side of the code.

Let’s decode your mailbox options together. Contact us today and we’ll walk you through it.