CBU vs. 4C Mailboxes: Which Is Best for Your Property? – August 2025

For developers, property managers, and community associations, choosing the right mailbox system is more than just a design detail—it’s a USPS compliance requirement. In recent years, the Postal Service has moved toward centralized mail delivery, making CBUs (Cluster Box Units) and 4C mailboxes the most common solutions.

Both offer secure, efficient mail delivery, but they serve different purposes. Here’s how to decide which option is right for your property.

What is a CBU Mailbox?

A CBU, or Cluster Box Unit, is a freestanding, pedestal-style mailbox system designed for outdoor use. These units are USPS-approved and are the standard choice for many new residential communities.

Best suited for:

• Neighborhoods with single-family residences

• Housing developments, HOAs, or subdivisions

• Properties where outdoor mail delivery is most practical

Key features:

• Built for exterior installation

• Multiple locked compartments for individual residents

• Includes parcel lockers for package delivery

What is a 4C Mailbox?

A 4C mailbox is a centralized, wall-mounted mailbox system made for indoor settings such as apartment lobbies, clubhouses, or mailrooms. These mailboxes are the current USPS standard for interior installations and are often used in apartment renovations or new multifamily construction.

Best suited for:

• Apartments and condominiums

• Student housing complexes

• Office buildings and mixed-use properties

Key features:

• Designed for interior installation

• Flush- or surface-mounted in walls or cabinets

• USPS-compliant and built for secure resident access

The Key Difference: Interior vs. Exterior

The most crucial distinction between CBUs and 4C mailboxes is where they are installed:

• CBU Mailboxes: Outdoor, pedestal-mounted, ideal for single-family communities

• 4C Mailboxes: Indoor, wall-mounted, ideal for apartments, clubhouses, and lobbies

Both types meet USPS regulations for centralized delivery. The decision depends on your property’s layout, resident needs, and whether the mail delivery point will be inside or outside.

Mixed Solutions for Student and University Housing

In some instances, such as student housing and university properties, a combination of both CBUs and 4C mailboxes works best. CBUs may serve townhome-style or dormitory units, while 4C mailboxes provide secure indoor delivery in apartment-style housing or campus mailrooms.

This flexible approach helps accommodate diverse building types while maintaining USPS compliance.

Choosing the Right Mailbox for Your Development

Developers and property managers should consider:

• USPS requirements for centralized delivery

• Indoor vs. outdoor installation options

• Resident convenience and accessibility

• Long-term durability and security

FAQs for CBU vs. 4C Mailboxes

What does CBU stand for?

CBU stands for Cluster Box Unit, a freestanding, outdoor mailbox system approved by USPS for centralized mail delivery in single-family residential communities and similar developments.

What is a 4C mailbox?

A 4C mailbox is a wall-mounted, centralized mailbox system designed for indoor use in apartment lobbies, clubhouses, mailrooms, and multifamily housing. It is the current USPS standard for interior installations.

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

The main difference is installation location: CBU mailboxes are installed outdoors for single-family neighborhoods, while 4C mailboxes are installed indoors for multifamily buildings, clubhouses, and mailrooms.

Which mailbox system is best for developers?

Developers should choose based on property type:

• CBUs are best for single-family housing developments or HOAs.

• 4C mailboxes are ideal for apartments, condominiums, and renovations.
  Some properties, such as student or university housing, may benefit from using both.

Are CBUs and 4C mailboxes USPS-approved?

Yes. Both CBUs and 4C mailboxes are USPS-approved for centralized delivery. USPS requires these systems in most new developments and multifamily renovations.

Can student housing use both CBU and 4C mailboxes?

Yes. Student and university housing often uses a mix of both. CBUs can serve townhome- or dorm-style residences, while 4C mailboxes provide indoor delivery for apartment-style housing or campus mailrooms.

Contact Select Commercial Mailboxes

At Select Commercial Mailboxes, we provide a full range of USPS-approved CBUs and 4C mailboxes designed for residential communities, multifamily housing, student developments, and more.

Contact us today to find the right mailbox solution for your property and ensure your project meets postal requirements.