Mail Slots and Through Wall Mailboxes

What Is a Mail Slot?

A mail slot is a narrow opening installed in a door or wall that allows mail to be delivered directly into a home or building. Also called a letter slot or letter plate, mail slots are a practical alternative to curbside mailboxes, especially in areas with walk-up delivery service.

For more background on residential mail slot options, see our residential mail slots blog.

Mail slots have been a fixture of residential architecture for well over a century. They remain popular in urban row homes, historic properties, and renovation projects where a curbside post is not practical or permitted by HOA guidelines.

Types of Mail Slots

Not all mail slots are installed the same way. The right type depends on your door construction, wall material, and whether you want a front door mail slot, a wall mail slot, or mail routed through the wall entirely. 

Here is how the three main configurations compare and when each one makes sense. For a broader look at how mail slots fit into the wider mailbox landscape, see our types of mailboxes guide.

Mail Slot Materials and Finishes

MailboxWorks carries mail slots in two primary materials: stainless steel and solid brass. Each suits a different aesthetic and maintenance preference.

Stainless Steel Mail Slots

• Aesthetic: Contemporary, clean
• Finish options: Brushed, polished
• Weather resistance: Excellent
• Maintenance: Minimal
• Made in USA: Select models
• Customization: Not available

Brass Mail Slots

Available from our Streetscape brass mailboxes line, with optional brass house numbers and address plaques welded directly to the mail slot.

• Aesthetic: Traditional, premium
• Finish options: Natural brass, unlacquered (develops patina over time)
• Weather resistance: Excellent
• Maintenance: Zero maintenance required; patinas naturally over time
• Made in USA: Yes, Streetscape Executive, hand-cut and welded in Huntington Beach, California
• Customization: Brass house numbers available, welded directly to the mail slot

Choosing the Right Mail Slot Size

Mail slots come in three size classes. The right choice depends on your typical mail volume and whether you regularly receive oversized envelopes or catalogues.

USPS sets a minimum slot opening of 1.5 inches high by 7 inches wide for a standard mail slot for door installations. If you’re specifying a locking or secured design, the opening requirement increases. 

Most single-family homeowners do well with a letter-size slot. Pairing your slot with a mail slot cover or interior catcher keeps mail tidy and the opening protected when not in use. If you’re in a household that regularly receives large-format mail or runs a home business, sizing up to magazine or large is worth the minimal added cost. Need to replace worn hardware on an existing install? Browse our mailbox replacement parts.

USPS Mail Slot Requirements

USPS mail slot requirements set specific standards for door and wall mail slots in residences served by walk-up delivery. Key requirements:

• Minimum opening: 1.5 inches high x 7 inches wide for standard door slots
• Locked mail slot designs: Minimum opening 1.75″ x 10″ per USPS standards
• Bottom of slot height: Minimum 30 inches from the floor or ground level
• Horizontal slots: Must be hinged at the top
• Vertical slots: Must be hinged on the side opposite the door’s hinges
• Walk-up delivery eligibility: Not all addresses qualify. Check with your local postmaster before specifying a mail slot as your primary delivery point.

Getting mail slot size right from the start avoids costly reinstallation. For the complete regulatory reference, see the USPS mailbox installation guide. For a deeper breakdown of residential and commercial mailbox compliance, our USPS mailbox regulations guide covers the full picture.

These requirements apply to standard residential mail slots. Commercial installations and locked designs may have additional specifications under USPS Engineering Standards 7B and 7C.

Mail Slot Security and Insulation Tips

Mail slot security is a legitimate consideration. Mail slots do introduce an opening in an otherwise sealed door or wall, and a few targeted measures cover both security and energy efficiency. For a broader look at burglar-proofing a mail slot, SafeWise offers practical guidance on securing a door mail slot.

Interior mail catchers and baskets are the first line of defense. A catcher that mounts flush to the interior side of the slot prevents anyone from fishing through the opening, keeps mail off the floor, and reduces visible light from outside. Most residential mail slot installations should include one.

Interior flap design matters. Look for slots with a tight-fitting, spring-loaded interior flap rather than a loose cover. The tighter the closure, the less exposed the interior and the better the draft seal.

Insulated mail slots are available for energy-conscious installations. These include an insulating brush or foam seal behind the flap that reduces air exchange without impeding mail delivery.

For higher-security needs, particularly in apartment buildings or commercial entries, a locking mailbox or parcel mailbox and drop box may be the more appropriate specification. A mail slot is a convenience feature; it does not provide parcel security or mail theft protection. If both are priorities, a wall mount mailbox with a locking door is worth comparing.

Why Choose Our Mail Slots at MailboxWorks

Trusted by thousands of homeowners and rated five stars by our customers, MailboxWorks carries a curated selection of door and through-wall mail slots in both stainless steel and solid brass, vetted for USPS compliance, build quality, and entryway design compatibility. The catalog covers specification-grade products from Salsbury Industries, Architectural Mailboxes, and Streetscape Executive, skipping the commodity tier entirely.

Every residential mail slot in our catalog ships free on orders over $30. Our brass Streetscape Executive line is handcrafted in the USA, a specification-grade option for historic preservation projects, custom builds, and buyers who want hardware that holds up long-term.

Trusted by clients including the Department of Defense, Harvard University, NBC, and Major League Baseball for commercial and institutional mailbox programs, MailboxWorks brings the same product depth to residential specifications. 

Questions about which mail slot for door or wall installation suits your project, door thickness compatibility, USPS requirements for your delivery zone, or finish matching? Call our mailbox specialists at 1-866-717-4943 or browse the full residential mailboxes catalog above.