This site uses cookies to deliver a better experience.


An Introduction to the Different Types of Mailboxes

Friday November 26, 2021

The United States Postal Service (USPS) is responsible for delivering mail to over 160 million addresses per year. Some of these addresses consist of homes or apartments, whereas others consist of businesses and commercial properties. Regardless, they all have a mailbox where USPS couriers can drop off mail. There are many different types of mailboxes, however. While you might be familiar with traditional curbside mailboxes, you might be surprised to learn about the alternative mailboxes supported by the USPS.

Traditional Curbside

As shown in the image above, a traditional curbside mailbox is defined by shape. It features a rectangular-dome shape, which has become synonymous with curbside mailboxes. Traditional curbside mailboxes have a hollow interior with a door on the front. When delivering mail, USPS couriers can open the door to leave the resident's or business's mail.

Contemporary Curbside

There are also contemporary curbside mailboxes. Contemporary curbside mailboxes don't feature the same rectangular-dome shape as their traditional counterparts. Rather, they feature an alternative shape. Some of them are oval, whereas others are square. Regardless, USPS classifies all curbside mailboxes that don't feature a rectangular-dome shape as being contemporary.


The USPS supports the use of Cluster Box Units (CBUs) for certain residences and properties. They've been around for several decades, with the latest CBU specification emerging in 2007. CBUs are different from curbside mailboxes because they are a centralized mail delivery system. Whether traditional or contemporary, all curbside mailboxes support a single address. CBUs, on the other hand, support multiple addresses. CBUs feature multiple small mailboxes in a single large unit.


Another common type of mailbox is STD-4C. STD-4C is a specification for wall-mounted centralized mail delivery units. They are similar to CBUs but with a few caveats. For starters, all STD-4C mailboxes are required to have at least one parcel locker per 10 mailboxes. If an STD-4C has 20 mailboxes, for example, it must have two parcel lockers. The STD-C mailboxes are also required for all new multi-unit building plans. Property developers can't use curbside mailboxes, nor can they can use CBUs. For new building plans with multiple addresses, the USPS requires developers to use STD-4C mailboxes.

Door Slot

While technically not a mailbox, the USPS allows door slots to be used as for mail delivery. A door slot is a narrow and horizontal opening on a door that allows USPS couriers to deliver mail to the respective address. The downside to door slots is that they don't support the use of outgoing mail. Mail couriers can deliver mail by inserting it through a door slot, but they can't collect outgoing mail through a door slot.


About Forsite:

Welcome to Forsite! You’ve found your best source of custom street signs and community wayfinding signs. We manufacture and install upscale site amenities throughout the United States.

Forsite can provide all of your signage needs for your Master Planned Community or  Residential Development. We help our customers to create a uniform, upscale appearance and increase property values by "bundling" themed packages of decorative street signage, mailboxes, post and wall mounted lighting, and wayfinding signage

You can count on the experts at Forsite to help improve the quality of your community today. Contact us today to get started by talking to one of our experienced team members at 855-537-0200.