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USPS Mailbox Requirements for New Construction

When building a new multi-family or commercial development that will receive USPS mail delivery, choosing a USPS-approved mailbox system is not optional — it is a postal service requirement. Before your project is complete, your local postmaster must approve the mailbox installation plan.

Key USPS requirements:

• 4C horizontal mailboxes are required for new multi-family construction. Any new apartment building, condominium, or multi-unit residential development must install USPS-STD-4C-compliant horizontal mailboxes.
• One compartment per unit — each tenant must have a dedicated, individually locked compartment.
• Parcel locker ratio — at least one parcel locker for every 10 tenant compartments.
• Accessibility compliance — bottom compartments no lower than 28 inches; top no higher than 67 inches from the floor.
• Postmaster pre-approval — submit your installation plan to your local postmaster before installation. Installing without approval can result in USPS refusing to deliver mail to the property.

US Mail Supply can walk you through these requirements and help prepare postmaster documentation.

New Construction Mailbox Types: Indoor & Outdoor Options

• 4C Horizontal Mailboxes (Indoor) — USPS standard for new multi-family construction. Wall-recessed or surface-mount in lobbies and mail rooms. Modular for any unit count.
• Cluster Box Units / CBUs (Outdoor) — For garden apartments, townhomes, and low-rise communities. 4, 8, 12, and 16-door configurations with parcel lockers. Pedestal included.
• 4B+ Vertical & Horizontal Mailboxes (Indoor) — Primarily for replacement; applicable to some new commercial projects. Surface-mount and recessed.
• Decorative Column & Wall-Mount Mailboxes — For single-family home communities where individual mailboxes are preferred.

USPS-Approved Mailboxes for Every Development Type

• Apartment complexes and condominiums — 4C horizontal for new builds; CBUs for outdoor communities
• Townhome and single-family home communities — outdoor CBUs or decorative column mailboxes
• Commercial office buildings — 4C or 4B+ wall-mount systems
• Mixed-use developments — combination residential, commercial, and parcel locker systems
• Hospitals and healthcare facilities — secure indoor systems
• Military housing and government facilities — USPS-compliant to government specs

All systems ship nationwide. We provide installation documentation and postmaster submission support.

Commercial

USPS delivery & private delivery

Shop indoor and outdoor mailboxes for apartment complexes, condos, offices, colleges, or local businesses. Choose high end vintage style large cluster mailboxes or simple small indoor lockable horizontal mailboxes for a lobby area or entryway.

Indoor

Invest in quality

Our inventory features horizontal and vertical indoor metal mailboxes for commercial buildings and businesses. Equip a small apartment complex or an entire university with secure storage for mail, internal documents or packages – USPS approved or private use options available.

Mailroom

Totes, shelves, sorters, and more

We supply professional mailroom supplies and equipment for commercial and municipal buildings. Choose from our wide selection of mailroom totes, sorters, shelves, carts, and more.

4C Horizontal

USPS 4C horizontal & 4C depot style boxes

We supply Florence 4C horizontal and 4C depot style mailboxes for commercial and municipal buildings for a highly secure option. Horizontal 4C mailboxes are USPS approved (STD-4C) and 4C depot style mailboxes are for private deliveries only.

USPS Approved

Commercial, Apartment, & Residential Units

The U.S. Postal Service will only deliver to your mailbox if it's up to their standards – including box size, location, slot dimensions and identification info. Our USPS approved mail boxes include easy installation instructions to ensure you meet all official guidelines.

Residential

Quality one-time purchase

Cheap home mailboxes are flimsy and put your belongings at risk. For single-house rentals or individual home owners, a metal mailbox poses the best security and defense. Choose a wall mounted mail house or traditional locking box with post.

Outdoor

Apartments, schools, or businesses

Outdoor metal mailboxes with secure locking options protect possessions from theft and harsh weather. Choose decorative or standard cluster box units or locking residential mailboxes (USPS approved or for private use only).

Drop Boxes

Parcel & package receptacles

Florence drop boxes for parcels, packages, and mail are always sturdy and secure. Your packages and letters will be kept safe until your mailman arrives to collect the contents.

Frequently Asked Questions About USPS-Approved Mailboxes for New Construction

What USPS-approved mailboxes are required for new construction?

For new multi-family residential construction, 4C horizontal mailboxes are required under USPS-STD-4C (the standard since 2006). For outdoor low-rise communities like townhomes and garden apartments, cluster box units (CBUs) are the USPS-approved alternative. Your local postmaster confirms which system is required for your specific development.

Do I need postmaster approval before installing a new construction mailbox?

Yes — postmaster pre-approval is required. You must submit your installation plan (mailbox type, placement, height, layout) to your local USPS postmaster before installation. USPS can refuse mail delivery if the system was installed without prior approval. US Mail Supply can help prepare the required documentation.

How many mailbox compartments do I need for my new development?

USPS requires one individually locked compartment per tenant unit, plus at least one parcel locker for every 10 compartments. A 30-unit building needs 30 compartments and 3 parcel lockers minimum. We can configure modular 4C systems for any unit count.

What is the difference between a 4C mailbox and a CBU for new construction?

4C mailboxes are indoor, wall-mounted systems for buildings where mail is delivered inside. CBUs are outdoor, pedestal-mounted systems for communities where mail goes to a central exterior location. Your postmaster determines which applies.

Are there ADA requirements for new construction mailboxes?

Yes. Bottom compartments must be at least 28 inches from the finished floor; the top of the highest compartment must not exceed 67 inches. Outdoor pedestal systems have separate USPS height-from-curb requirements.

Can I use a 4B+ mailbox for new construction?

4B+ is primarily for replacement installations. New multi-family residential construction requires 4C. Some new commercial projects may accept 4B+ — confirm with your local postmaster before specifying.

How long does it take to get new construction mailboxes delivered?

Standard in-stock items ship within a few business days. Custom configurations may need additional time. Order 4–6 weeks before planned installation to allow for postmaster approval and schedule adjustments.

Does US Mail Supply provide documentation for postmaster submission?

Yes — we provide product data sheets, installation specs, and compliance documentation. Our team has extensive experience supporting construction projects through the postmaster approval process.