USPS-approved 4C cluster mailbox units for multi-tenant buildings — from 8-door units for smaller properties to 16-door configurations for large apartment complexes. Indoor surface-mounted, recessed, and outdoor pedestal installations by RPS Building Specialties across Southern California.
From compact 8-door units for smaller properties to 16-door configurations for large apartment complexes, we supply the full range of USPS-approved 4C cluster mailbox units.
8 tenant compartments + 2 parcel lockers + 1 outgoing mail slot. Front-loading, aluminum construction. Ideal for smaller properties and retrofit installations.
12 tenant compartments + 2 parcel lockers + 1 outgoing mail slot. Most popular configuration for apartment retrofits. Mid-size multi-tenant buildings.
13 tenant compartments + 3 parcel lockers + 1 outgoing mail slot. USPS standard for new construction clusters. Standard configuration.
16 tenant compartments + 2 parcel lockers + 1 outgoing mail slot. Maximized tenant capacity for large complexes. Efficient tenant-to-unit ratio.
Wide format with multiple rows of compartments side by side. Ideal for wide lobby walls and mailroom installations.
Tall format with stacked compartments in columns. Space-efficient for narrow lobbies and hallways.
Choosing the right material determines your cluster mailbox's durability, appearance, and compliance — especially in Southern California's diverse climate zones.
All cluster mailbox installations must meet USPS Standard 4C requirements. Here is what you need to know for your project.
Standard 4C cluster box unit configurations. RPS provides free site assessments to determine the optimal configuration for your building.
An honest look at RPS cluster mailbox installation capabilities and what falls outside our scope.
Cluster mailboxes are the standard centralized mail delivery solution for multi-tenant residential and commercial buildings across Southern California. Whether you are constructing a new apartment complex, retrofitting an older building, or replacing outdated individual mailboxes, USPS-approved 4C cluster box units provide secure, efficient mail delivery for every tenant in your property. As centralized delivery becomes the norm for all new construction, selecting the right cluster mailbox configuration is one of the most important decisions in your building's postal infrastructure.
Since June 2004, USPS Standard 4C has mandated centralized delivery for all new construction and major renovations. This means every new multi-tenant building must install USPS-approved cluster box units rather than individual door-delivery mailboxes. The 4C standard requires integrated parcel lockers in each cluster unit, an outgoing mail collection slot, and a master arrow lock for USPS carrier access. Compliance is not optional — your local USPS postmaster must approve the cluster mailbox location and configuration before installation, and non-compliant installations will not receive mail service.
Cluster mailboxes can be installed in several configurations depending on your building's layout and requirements:
Standard 4C cluster mailbox units are manufactured from aluminum, which is the USPS standard material. Aluminum is lightweight, naturally corrosion-resistant, and performs well in Southern California's coastal and inland environments. For high-traffic locations or vandal-prone areas, stainless steel front-loading units provide premium durability. Powder-coated finishes in sandstone, dark bronze, black, postal grey, and white are the standard color options. Most property managers choose sandstone or dark bronze for their ability to complement a wide range of building exteriors and hide minor scuffs from daily use.
If your building requires additional mail and package infrastructure beyond cluster mailboxes, RPS Building Specialties also supplies and installs parcel lockers for high-volume package delivery, commercial mailboxes for individual tenant mailbox installations, and commercial lockers for tenant package pickup. Contact us at (714) 381-4196 or [email protected] for a free site assessment and project quote.
Common questions about 4C cluster mailbox units answered by our postal product specialists.
A 4C cluster mailbox unit is a USPS-approved centralized mail delivery system that serves multiple tenants from a single installation. Units are available in 8-door (8 tenant compartments + 2 parcel lockers), 12-door (12 + 2), 13-door (13 + 3, USPS new construction standard), and 16-door (16 + 2) configurations. Every unit includes an outgoing mail collection slot. The "4C" refers to USPS Standard 4C, which mandates centralized delivery for all new construction and major renovations since 2004. Florence and Salsbury Industries are the leading manufacturers of 4C-compliant cluster box units.
The number of tenant units determines your cluster box configuration. Count total tenant spaces (apartments, offices, suites), then select cluster box units that match. For example, a 24-unit apartment building might use two 12-door units or a combination of 8-door and 16-door units. Factor in parcel locker capacity — buildings with high package volume may need additional parcel compartments. Consider indoor vs. outdoor installation location, available wall or floor space, and ADA accessibility requirements. RPS Building Specialties provides free site assessments to recommend the optimal configuration.
Indoor recessed cluster mailboxes are set into a pre-cut wall opening so only the face of the unit is visible — creating a clean, flush appearance in building lobbies. The wall opening must be prepared by a general contractor to manufacturer specifications before RPS installs the unit. Outdoor pedestal-mounted cluster mailboxes are freestanding units secured to a pedestal base, which is bolted to an existing concrete pad with expansion anchors. Outdoor installations require a USPS-approved weather shelter or canopy for protection. RPS handles both installation types — surface-mounted pedestal installations and recessed unit installations into prepared openings.
Standard 4C cluster mailbox units are available in powder-coated aluminum finishes including sandstone, dark bronze, black, postal grey, white, and gold. These are the most common finishes for commercial installations. Premium options include stainless steel front-loading units for vandal-resistant applications in high-traffic locations. The powder-coated aluminum finishes are factory-applied and designed to withstand outdoor weather exposure. Most property managers choose sandstone or dark bronze as these colors complement a wide range of building exterior colors and hide minor scuffs from daily use.
Yes. USPS requires that the local postmaster approve the cluster mailbox location and configuration before installation. This includes verifying that the location provides adequate carrier access, lighting, weather protection (for outdoor installations), and ADA-compliant mounting heights. The approval process also confirms the correct number of tenant compartments, parcel lockers, and outgoing mail collection. RPS Building Specialties coordinates with your local USPS postmaster as part of our installation process to ensure your cluster mailbox meets all approval requirements before we install.