Salsbury 4C Horizontal Mailboxes: Sizes, Styles & Configurations Explained
September 18, 2025
If you’re in the market for mailboxes, Salsbury 4C horizontal mailboxes provide USPS-approved, heavy-duty mail solutions for centralized delivery in commercial, residential, and institutional settings. They are compliant with USPS STD 4C regulations, required for new construction and major renovations since October 2006.
It can be overwhelming trying to decide between different sizes, styles, and configurations of mailboxes. This guide will break down everything you need to know about Salsbury 4C horizontal mailboxes so you can make the right decision for your community.
Understanding USPS STD-4C Standards
USPS STD-4C standards are mandated mailbox specifications for new builds. Since 2006, they have improved mail security, accessibility, and durability. One of the key requirements is that there must be at least one parcel locker for every five tenant compartments. This will make your tenants happy, as their packages will be secure in spacious parcel lockers instead of being left on the floor of your building’s vestibule or lobby.
These requirements also improve accessibility. The USPS arrow lock (master door lock) should be located between 36 and 48 inches above the finished floor. The bottom of the lower mailbox should be no less than 28 inches, and parcel lockers should be no less than 15 inches from the finished floor.
Available Sizes & Door Dimensions
Determining what size your community will require is one of the toughest parts of shopping for mailboxes. Salsbury 4C horizontal mailboxes come in a wide variety of sizes and door dimensions. Standard MB mailbox door sizes include MB1 (13 ¼”W×3 ¼”H), MB2 (13 ¼”W×6 ¾”H), MB3 (13 ¼”W×10 ¼”H), and MB4 (13 ¼”W×13 ¾”H). Parcel lockers are also available in varying sizes, including PL3: (10 ¼”H), PL4 (13 ¾”H), PL4.5: (15 ½”H), PL5 (17 ¼”H), and PL6: (20 ¾”H).
Mailbox Door Sizes
Parcel Door Sizes
No matter what your size requirements are, you will be able to find 4C horizontal mailboxes that are just right for your community with Salsbury Industries.
Configurations & Mounting Styles
Salsbury 4C horizontal mailboxes are available in configurations that are 1 door wide (single column) and 2 doors wide (double column). They come in 4 different heights: 6 door high, 10 door high, 11 door high, and Maximum Height (56 ¾” H) units.
They also come in three different mounting styles. Recessed mounted mailboxes are built into the wall for both indoor and outdoor use. Surface mounted mailboxes are affixed to wall surfaces via an enclosure. This is ideal where wall depth is limited. Free-standing mailboxes are stand-alone framed units that offer flexibility in terms of placement.
If none of these options seem right for your community, Salsbury also offers 4C custom horizontal mailboxes. Our custom configurations include combinations of mailbox and parcel locker sizes, a wide array of color options, and ADA-compliant designs.
Brand & Build Quality?
Constructed with heavy-duty aluminum and stainless-steel hardware, Salsbury 4C horizontal mailboxes offer durability and will require minimal maintenance over time. They also feature powder-coated finishes in aluminum, bronze, black, and sandstone. Custom colors are available as well.
Our USPS-approved 4C horizontal mailboxes come with built-in heavy-duty cam locks for added security with dust/rain shields. They also include anti-fish plates to prevent tampering and outgoing mail compartments with a weather protection flap.
If you have any issues with your mailbox, all Salsbury 4C horizontal mailboxes come with a 5 year warranty.
Installation Guidance & Tools
When you install mailboxes, it’s important that they meet ADA and USPS clearances. If not, USPS mail carriers might stop delivering to your community. Pay attention to the placement of arrow locks and compartment heights in order to meet requirements. Our United States Postal Service Mailbox Regulations and Specifications page will help guide you through how to navigate these regulations.
Our Mailbox Configurator tool helps stakeholders design units and includes elevation drawings, rough-in dimensions, BIM/Revit models, and quote requests. We offer design support to architects and product planners. Salsbury Industries provides a complete library of Mailbox Revit files, Mailbox AutoCAD blocks, and Mailbox SPECS. We also offer additional product information that includes installation instructions and technical drawings.
Ideal Use Cases
Salsbury 4C horizontal mailboxes are best suited for multi-family residential communities, commercial buildings, schools, government facilities, military, universities, and private postal centers. As you can see, there is a wide array of uses for these mailboxes.
There are many advantages to using Salsbury 4C horizontal mailboxes. Centralized mail management is easier on mail carriers since they only have to deliver mail to one location instead of several, and results in greener neighborhoods. Parcel lockers ensure secure parcel delivery rather than leaving packages in a building’s vestibule or lobby where they might be stolen. These mailboxes also offer tamper resistance, durability, and aesthetic flexibility.
Customization & Extras
There are many ways to customize Salsbury 4C horizontal mailboxes so that they will suit your needs. 1-¾” W x 1-½” H custom engraved placards are available as an option upon request. You can also opt for adhesive numbering, mail slot plug kits, replacement locks, and additional keys. Surface mounted and free-standing units are available as well, and add flexibility in installation.
As you undergo new construction or major renovations, it can be difficult deciding on which 4C horizontal mailboxes would be best suited to your community. Even once you decide on Salsbury Industries, there are still many more decisions to be made regarding size, styles, and configurations. Hopefully, this guide has helped you understand how Salsbury 4C horizontal mailboxes efficiently combine USPS compliance, durability, security, and versatility, and given you the knowledge you need to move forward.
You don’t need to worry if you have very specific mailbox needs. Our Mailbox Configurator will help you determine the optimal number of mailboxes and parcel lockers for your community based on your requirements. The 4C Mailbox Configurator provides a summary with elevations, rough opening dimensions, sample installation instructions, model numbers, and other helpful information. Try it out today!