USPS Approved Cluster Mailboxes

What Are USPS-Approved Cluster Mailboxes (CBUs)?

Cluster mailboxes, also known as Cluster Box Units or CBUs, are centralized, pedestal-mounted mail units used for secure mail and package delivery in multi-tenant residential and commercial properties such as apartment communities, HOAs, and mixed-use developments. Each unit has its own locked compartments for tenants and is built to meet USPS STD-4C requirements.

When comparing cluster mailbox options, buyers typically review door count, parcel locker capacity, finish options, and lead times. While the equipment itself meets USPS manufacturing standards, the installation location and placement must be coordinated with and approved by the local postmaster to ensure proper accessibility for mail delivery.

​Choose the Right Cluster Mailbox Size

Selecting the correct size depends on your current tenants and whether that number is likely to grow. Most apartment buildings use a few common mailbox sizes, which are listed below.

• 8-door units – Best for small properties with fewer residents.
• 12-door units – Often used in medium-sized buildings.
• 13-door units – Chosen often because the layout works well.
• 16-door units – Used where tenant count and mail volume are higher.

Smaller configurations are available, but they aren’t used very often. Many property managers choose a slightly larger size so there’s room for more tenants or more packages later. Adding units later may require additional USPS coordination and separate installation.

​Parcel Lockers and Package Delivery (Built-In or Standalone)

Parcel lockers support unattended package delivery when items do not fit inside standard mailbox compartments.

When a package is too large for a tenant’s mailbox, the carrier places it in an available parcel locker and deposits the locker key into the recipient’s individual mail compartment. The resident retrieves the package using the key. Once the locker door is opened, the key remains in the lock for carrier reuse.

Buyers typically encounter two parcel locker options in this category:

• Cluster mailbox units with integrated parcel lockers
• Standalone outdoor parcel locker units installed alongside CBUs as package volume increases

Standalone parcel lockers are commonly used to expand capacity over time.

​USPS Access and Security Features to Expect

USPS-approved cluster mailboxes are designed for secure, consistent delivery and include standardized features required for daily use.

Common features include:

• Front-loading master access doors for postal carriers
• Preparation for a USPS arrow lock, the standardized master lock system used nationwide
• Individually locked tenant compartments
• Outgoing mail slots on applicable models
• Weather-resistant finishes for outdoor installations

While cluster mailboxes meet USPS manufacturing standards, the installation location and placement must be approved by the local postmaster. USPS arrow locks are installed by postal officials after placement and provide authorized carrier access.

​Materials, Style, and Outdoor Durability

Cluster mailboxes are made for outdoor use. They use corrosion-resistant materials and durable powder-coated finishes to handle sun, rain, and temperature changes.

In some properties, units may be installed in covered or protected mail areas, depending on site layout and USPS placement requirements. Construction and finish options are selected to support long-term use while maintaining a consistent appearance within the community.

Color Options and Door Numbering (Decals vs Engraving)

Cluster mailboxes typically come in five or six standard powder-coated finishes. The available options depend on the manufacturer and model and are often chosen to meet architectural or HOA guidelines.

Door numbering options typically include standard adhesive decals or engraved numbering for a more permanent identification method. Availability of finishes and numbering options should be reviewed at the product level.

​Pedestals, Mounting, and Planning for Installation

Cluster mailboxes include matching aluminum pedestals as standard equipment to ensure proper installation height and USPS compliance. Installation planning should account for accessibility, clearance, and long-term placement.

Final placement must be coordinated with and approved by the local postmaster, especially for new construction or community developments. Early confirmation helps ensure compliance and avoid relocation.

Shipping, Lead Times, Discounts, and Warranty

Shipping timelines vary by configuration and availability. Stock models may ship quickly, while custom options such as specific finishes or engraved numbering may require additional production time.

MailboxWorks supports larger projects with volume pricing and manufacturer-backed warranty coverage. Product pages provide the most accurate details on availability and lead times.