What Is a 4C Recessed Mailbox?

A recessed mailbox is any mail receptacle designed to be installed flush into a framed wall opening, with the front face sitting level with the surrounding wall surface rather than projecting outward. In commercial and multi-tenant buildings, recessed mailboxes are the recognized standard for centralized mail delivery in new construction.

Also referred to as indoor mailboxes or wall-mounted mailboxes in multi-tenant settings, these units most commonly refer to a 4C horizontal system governed by USPS STD-4C, the federal standard for centralized mail delivery in new builds and major renovations since October 2006. These USPS approved wall mount mailboxes serve as permanent indoor mail systems for apartments, condos, office buildings, military bases, university housing, and multi-family developments. They're also commonly chosen to replace older 4B horizontal installations during renovation projects.

Recessed mounting is the only 4C configuration approved for USPS carrier delivery. 4C surface mounted mailboxes and private delivery mailboxes serve buildings using a private carrier rather than USPS. If your project requires USPS centralized delivery service, recessed is the required installation type.

In residential settings, recessed mailboxes serve as decorative wall mount mailbox slots, and vertical mailboxes cover 4B-format recessed alternatives for smaller or older multi-tenant buildings. Both are separate product categories from the 4C horizontal mailboxes featured on this page. If your project involves unaddressed mail or package delivery outside USPS requirements, cluster mailboxes or our full commercial mailboxes catalog may be the right starting point.

Planning Your Recessed 4C Mailbox Installation

Recessed installation requires more upfront coordination than surface or free-standing mounting. The wall opening has to be framed before the unit arrives, and USPS approval has to be secured before mail service can begin. Sorting out these details early prevents expensive rework after the unit is already built into the wall.

Rough Opening and Wall Depth Requirements

Planning the wall opening and wall depth is the first thing to sort out before framing begins for a recessed 4C installation. Your wall needs a minimum of 17 inches of clear depth to accommodate the unit, measured through the wall from the finished front face to the back of the cavity. It is not the stud depth alone. Account for drywall, finish materials, and any mechanical interference on both sides when calculating your available wall depth.

Rough opening dimensions vary by door height class. The tables below cover the Florence Versatile series across the full height range and the Salsbury 3700 series across its four standard heights. The dimensional spec sheet for each product is linked on its product page.

Florence Versatile Series

Salsbury 3700 Series - Front Loading

Front Loading vs. Rear Loading

Front loading is the standard configuration for recessed 4C installations. The USPS carrier accesses all tenant compartments through a single master door secured with a USPS Arrow lock, installed and controlled by USPS. Tenants access their individual compartment from the same front face using a separate cam lock and key.

A rear loading recessed mailbox works differently. Mail is loaded from a secured room behind the wall, while tenants still retrieve from the front. This configuration suits buildings where a dedicated postal room is already part of the design, directly behind the mailbox installation. It requires a carrier-accessible, secured space on the back side of the wall.

If your building has no dedicated mail room, front loading is the practical choice. If you're designing a new building with postal infrastructure already in the plans, rear loading can improve delivery flow by keeping carrier and tenant traffic fully separated. For projects where a wall installation is not feasible at all, 4C free-standing mailboxes offer a separate mounting option worth reviewing. Not sure which configuration fits your project? Call us at (866) 707-0008 before ordering.

USPS Postmaster Approval

Every recessed 4C installation serving USPS delivery requires local postmaster approval before mail service begins. Your local postmaster reviews the configuration, confirms USPS STD-4C compliance, and coordinates the USPS Arrow lock installation. USPS installs and retains control of the master door lock. You purchase the mailbox; USPS supplies and owns the Arrow lock hardware.

Contact your local postmaster before purchasing, not after. Confirm your planned door count, parcel locker ratio, and mounting location. If the configuration needs to adjust based on that conversation, you want to know before the unit is built into the wall. See our USPS approved mailboxes resource for a fuller overview of the STD-4C compliance framework.

Choosing the Right Configuration

The right 4C recessed mailbox depends on three variables: how many tenant compartments your project requires, what parcel locker ratio your postmaster expects, and which 4C door height class fits your wall space. Most commercial recessed mailbox projects, including apartment complexes, condominiums, office buildings, military housing, university dorms, and multi-family residential developments, fall within a standard configuration range. The details vary by unit count and site-specific USPS requirements.

Whether you're specifying apartment mailboxes for a USPS-approved installation or sourcing multi-family mailboxes for a large residential development, the selection process follows the same steps. Start with your tenant count, confirm your parcel locker ratio with the local postmaster, and match your door height class to the available wall space. For indoor mailbox installations in lobbies or mail rooms, also factor in ceiling height and ADA compliance requirements before finalizing your configuration.

Door Height Classes

4C recessed mailboxes are available in door height classes from 6H through 16H, in both single-column and double-column configurations. The 4C door height class determines the total number of tenant compartments per unit and the rough opening dimensions required.

For projects with accessibility requirements, ADA compliant 4C mailbox configurations are available as MAX suites. These position larger door openings within the compliant height range. USPS STD-4C requires the floor of the lowest tenant compartment to be at least 28 inches above the finished floor. ADA Standards for Accessible Design (Section 308) sets the maximum forward reach at 48 inches above the finished floor, which governs top row placement. If your project involves accessible design compliance, confirm MAX suite availability when configuring your order.

Parcel Locker Requirements

USPS STD-4C guidelines require one 4C parcel locker for approximately every five tenant mailboxes. All preconfigured 4C recessed units available through Budget Mailboxes are built to meet this ratio. Confirm the specific requirement with your local postmaster before finalizing your configuration, as postmaster discretion can vary by facility.

For add-on parcel storage beyond what's included in a standard unit, see our 4C horizontal parcel lockers.

Available Colors and Finishes

Finish selection matters more than it might seem on a commercial project. The right finish helps the unit integrate cleanly with lobby materials, corridor walls, and HOA-specified color schemes rather than standing out as an afterthought. Both Florence and Salsbury use a powder coat finish applied over heavy-gauge aluminum, giving you a durable, scratch-resistant surface suited to long-term indoor installation.

Florence Versatile series offers eight standard 4C mailbox colors: Postal Gray, Silver Speck, Gold Speck, Black, Dark Bronze, White, Sandstone, and Antique Copper. Salsbury 3700 series covers four core neutrals: Aluminum, Bronze, Sandstone, and Black. If your project has specific architectural or HOA color requirements outside these standards, custom finishes may be available for larger orders. Call (866) 707-0008 to discuss options.

Features of Our Recessed 4C Mailboxes

Every 4C recessed mailbox in our catalog is built to USPS STD-4C specification, which sets minimum requirements for material quality, compartment dimensions, lock design, and durability. The structural frame on both Florence and Salsbury units is heavy-gauge aluminum. Individual tenant compartments are 300-series stainless steel, corrosion-resistant and significantly more durable than painted steel alternatives, particularly in high-traffic buildings. A weatherproof powder coat finish over the aluminum frame makes these units suited to both indoor lobbies and covered outdoor installations without performance trade-offs.

Each unit ships with a cam lock on every tenant door, fitted with a dust and rain shield and three keys per door. The outgoing mail slot includes an anti-fishing comb to block mail theft from the outside. Parcel lockers use a double-latching mechanism that locks automatically when the door closes, so the carrier does not need to manually re-secure it after each delivery. Interlocking and overlapping seams across the unit add a layer of tamper resistance that works alongside the lock hardware.

Door identification on any 4C recessed mailbox comes in two formats: number decals that accommodate up to 6 characters, or engraved identification that accommodates up to 12 characters. For buildings using unit numbers that combine letters and numerals, engraved identification is typically the right call.

Our Recessed 4C Mailbox Brands

Budget Mailboxes carries recessed mounted 4C horizontal mailbox systems from Florence and Salsbury, the two primary USPS-approved manufacturers for centralized mail delivery systems in the United States. Both brands meet STD-4C specifications, use heavy-gauge aluminum frames with 300-series stainless steel compartments, and are stocked and ready to ship.

Florence has manufactured commercial mailbox systems for over 80 years. Their Florence Versatile 4C series is the most widely specified recessed line in the U.S. market, offering eight standard powder coat finishes along with comprehensive BIM files and installation documentation suited to architect and general contractor workflows.

Salsbury Industries has manufactured commercial mailboxes since 1936. The Salsbury recessed mounted 4C horizontal mailbox line covers the full configuration range in four neutral finishes, built to the same construction standard as the Florence line. For projects where procurement simplicity and a proven track record matter more than color variety, Salsbury is a straightforward, well-documented choice.

Why Choose Budget Mailboxes for Your 4C Recessed Project

Budget Mailboxes is a trusted source for the recessed mailboxes that commercial and multi-family projects rely on, carrying both Florence Versatile and Salsbury 3700 configurations in stock, with free shipping on all orders and fast processing so your project stays on schedule. Volume pricing applies for orders of two or more units, making it a practical option for multi-building developments or phased construction timelines. Our team is available at (866) 707-0008 to help you confirm the right configuration before you order. Browse our full commercial mailboxes catalog, or scroll up to the product grid to start comparing recessed units directly.