Vertical Mailboxes | Commercial Recessed & Surface Mount Units

What is a USPS-Approved Vertical Mailbox?

Vertical mailboxes are USPS-approved mailboxes for replacement installs only: they meet USPS STD-4B+ and are authorized for one purpose, replacing existing 4B+ units like-for-like. If your building already has vertical mailboxes and you need to swap them out, you're in the right place. If you're planning new construction or a major renovation, USPS requires STD-4C compliance for all centralized mail delivery. Vertical units are not an approved option for those projects.

That distinction matters before you order. USPS STD-4B+ sets stronger compartment locks and master door requirements than the legacy 4B standard, which is why the units still hold approval for retrofit purposes. Your local postmaster must confirm the building qualifies for a like-for-like replacement before you purchase. Always verify that first.

USPS Approval Status for Vertical Mailboxes

As mentioned above, vertical mailboxes are USPS-approved mailboxes for one specific use: replacing existing 4B+ installations. If your building already has vertical mailboxes and you need to swap them out like-for-like, you're in the right place. If you're planning new construction or a major renovation, USPS requires STD-4C compliance for all centralized mail delivery. Vertical units are not an approved option for those projects.

The replacement-only rule traces back to October 2006, when USPS began requiring STD-4C compliance for all new construction and major renovations. Existing 4B+ vertical installations were grandfathered, so you can still replace them like-for-like, but you cannot specify a vertical unit for a building that does not already have one. Before you order, contact your local postmaster to confirm your building qualifies for a 4B+ replacement, and get that confirmation in writing where possible.

4B+ Vertical vs 4C Horizontal: Which One Do You Need?

The decision rule is short: if the wall opening already exists for a 4B+ vertical unit and you're not modifying the rough opening, 4B+ vertical mailboxes are your option. If you're building new, doing a major renovation, or changing the opening dimensions, you move to 4C horizontal mailboxes. Note that 4B+ and 4C units both use USPS arrow lock access, so master lock interoperability is not a factor in the decision.

For buildings where centralized outdoor delivery is the goal, cluster box units are worth reviewing alongside 4C options.

Recessed Mount and Surface Mount Vertical Mailbox Options

Both the Florence 1250 series and Salsbury 3500 series are available in recessed and surface mount configurations. Recessed installation requires a minimum 6-3/4-inch wall cavity for Florence 1250 units and a minimum 7-1/2-inch wall cavity for Salsbury 3500 units, for a flush, finished look. Surface mount is the right call when cutting into the wall isn't practical: the unit protrudes 6-7/8 inches from the wall surface (Florence 1250) or 7-1/2 inches (Salsbury 3500) requiring no cavity. Florence offers a surface-mount collar accessory for the 1250 series that gives the installation a cleaner transition at the wall face.

How Many Doors Do You Need for Your Building?

Selecting the right replacement vertical mailbox starts with one number: your tenant count. Units come in 3, 4, 5, 6, and 7-compartment configurations. These mailboxes are approved for replacement and retrofit installations only; for new construction or major renovations, 4C horizontal mailboxes are required. For buildings with limited wall width, units can be stacked two tiers high.

If your building needs an outgoing mail slot, order one additional compartment beyond your tenant count. Outgoing mail slot placement and configuration vary by manufacturer and should be confirmed at time of order.

Vertical Mailbox Features, Specifications, and Materials

• Construction: All-aluminum, anodized or powder coated finish

• Doors: Extruded aluminum with durable powder coated finish

• Locks: 5-pin cylinder cam lock per compartment; two keys included per lock; 1,000 key changes available

• Tenant identification: Name and number ID card holder per compartment; label included

• Loading type: Top-load/front-load; compartment array drops forward for carrier access

• Mounting: Available in recessed or surface mounted configurations

• USPS approval: Approved for replacement and retrofit installations only; not approved for new construction

Compartment dimensions vary by manufacturer:

Need to replace a damaged door? See our replacement parts & accessories for compatible parts.

USPS Access and Private Access Master Lock Options

Every USPS-approved vertical mailbox ships in one of two master lock configurations. USPS access units arrive without a master lock installed. Once the unit is in place and the postmaster has been notified, the postal carrier installs an arrow lock from USPS's own supply. You do not purchase or install the master lock yourself on a USPS access unit.

Private access units include a factory-installed commercial master lock with two keys. These are the right choice for buildings where in-house staff or a property manager handles mail distribution rather than direct USPS carrier delivery. If your building's access needs change, a postal-to-private conversion kit is available to switch between configurations without replacing the full unit.

Installation and Postmaster Approval Workflow

Before ordering 4B+ vertical mailboxes, work through these four steps to make sure your installation goes smoothly and USPS delivery begins without delays.

1. Contact your local postmaster before ordering. Confirm the building qualifies for a like-for-like 4B+ replacement. Get that confirmation in writing if possible.

2. Order the correct unit: recessed or surface mount, with the right door count for your tenant count. Verify wall depth before finalizing the recessed choice.

3. Install the unit. Vertical mailboxes are contractor-grade installs. Hardware is not included. The unit must be mounted in an indoor, weather-protected location: lobby, vestibule, or interior wall. The top-loading mechanism is not weather-sealed and should never be placed outdoors.

4. Notify USPS after installation. The carrier cannot begin delivery until the postmaster is informed the unit is in place. For USPS access units, the carrier installs the arrow master lock at this point.

For full carrier delivery requirements, refer to USPS Postal Operations Manual Section 632. For use cases within apartment mailboxes broadly, that page covers the full range of compliant options by building type.

Top Brands for Vertical Mailboxes

Florence Mailboxes: 1250 Series 

Florence Corporation has been the go-to manufacturer for small multi-family vertical mailboxes for decades. The 1250 series is built to USPS STD-4B+ standards and is available in recessed and surface mount configurations. Florence vertical mailboxes carry a 5-year manufacturer warranty and are backed by Budget Mailboxes as an authorized dealer.

Salsbury Vertical Mailboxes: 3500 Series 

The Salsbury 3500 series offers the same 4B+ compliance in a stackable format designed for buildings with limited wall width. Available in both recessed and surface mount, the 3500 series ships with the same 5-pin cam lock security standard. Salsbury vertical mailboxes include a 3-year manufacturer warranty and are available through Budget Mailboxes for both single-unit and bulk orders.

Why Choose Our Vertical Mailboxes

• Authorized dealer for Florence Corporation and Salsbury Industries, both manufacturers of USPS-approved vertical mailboxes

• 5-year manufacturer warranty on Florence units; 3-year manufacturer warranty on Salsbury units

• Bulk volume pricing available on orders of 2 or more units, ideal for multi-building property managers

• Compliance support by phone: our team can help you confirm the right configuration before you order

• Fast project quote turnaround on commercial and multi-unit orders

• Free shipping on qualifying orders

Ready to spec out your vertical mailboxes order? Request a bulk pricing quote and a member of our commercial team will follow up within one business day.