Choose a locking mailbox if mail theft happens on your street, if you receive checks, medications, replacement cards or tax documents at home, or if mail sits for days while you travel. Choose a non-locking box if none of those apply, because a locking box costs more, makes outgoing mail awkward (the carrier can't reach in), and is only as secure as the steel around the lock — a thin locking box is theater. A good locking box has a 16–18 gauge body, a steel (ideally stainless) latch, and a mail slot large enough for magazines: USPS requires at least 1¾" × 10" on approved locking curbside boxes.
Key facts
- Carriers don't carry keys to private locking boxes; mail goes in through a slot or a one-way door, and you retrieve it with your key.
- USPS-STD-7C: a Locked Mail Slot curbside box needs an opening at least 1.75" high × 10" wide.
- Gauge matters more on a locking box than any other: 16–18 ga body, steel latch.
- Adjustable-slot designs let you trade capacity for security.
- Outgoing mail: most locking boxes have no outgoing compartment; use a wall slot, a post office box, or hand it to the carrier.
How does a locking mailbox work with USPS?
The carrier delivers exactly as with a normal box — from the vehicle, into an opening. The difference is that the opening leads to a compartment only your key opens. Designs vary:
- Fixed slot. A horizontal slot in the front or top. Simplest; limited by slot size.
- Adjustable latch. The door opens a set distance (½" to 2", say) and no further unless unlocked. You choose the opening; bigger accepts magazines but lets a hand in further.
- Hopper / drop door. A pivoting tray that takes mail and dumps it into a locked chamber. Takes larger items; more moving parts.
- Parcel locker. Large locking box with a one-way parcel door. Usually a separate unit.
Carriers won't force oversized items through a slot; they'll leave a notice or deliver to the porch.
Is a locking mailbox actually secure?
Only if the box is. The lock is rarely the weak point; the sheet metal around it is. A 24-gauge locking box can be peeled open at the door corner with a screwdriver in seconds. Look for:
- Body and door of 16–18 gauge steel (0.048"–0.060").
- A steel latch or lock tab — stainless is ideal — rather than a zinc-alloy or plastic catch.
- Anti-fish design: a baffle, angled slot or adjustable opening that prevents reaching in.
- A cam lock with a real key (not a wafer lock that opens with a bent paperclip).
- Drainage and an interior finish, since locked boxes trap moisture.
See What Gauge Steel Is Best for a Mailbox?.
Comparison
| Non-locking | Locking | |
|---|---|---|
| Incoming mail security | None | Good to excellent (depends on gauge) |
| Outgoing mail | Yes (flag) | Usually no |
| Capacity | Full box | Reduced by slot / chamber |
| Large flats & padded mailers | Yes | Depends on slot size |
| USPS approval requirement | Standard | Slot ≥ 1¾" × 10" for approval |
| Cost premium | — | $50–$200 more |
| Failure modes | Rust, dents | Rust, dents, jammed lock, lost key |
| Appearance | Any | Slightly bulkier front |
Who should get a locking mailbox?
- You've had mail stolen, or neighbors have.
- You receive anything a thief can monetize: checks, prescription drugs, new credit or debit cards, tax forms, small electronics.
- You're away for days at a time and mail accumulates.
- You're on a rural route where the box is out of sight of the house.
- You're a small business receiving payments at home.
Who doesn't need one?
- Mail is mostly bills and catalogs and the street is quiet.
- You use Informed Delivery and collect mail daily.
- You have door delivery to a wall box inside a gated entry.
- You send a lot of outgoing mail from the box.
A non-locking box plus good habits (see How to Prevent Mail Theft) is enough for most households.
The tradeoffs to know before buying
- Outgoing mail. You'll need another way to send it. Some people keep a small wall slot at the door; USPS also lets you hand mail to the carrier or use collection boxes.
- Capacity. The locked chamber is smaller than the box looks.
- Keys. Get spares cut immediately; losing the only key means drilling the lock.
- Winter. Locks freeze. A dry graphite lubricant helps; so does a lock cover.
- Carrier goodwill. A slot that's too small means the carrier can't deliver flats, and the notices get old fast. Set an adjustable latch to the largest opening you're comfortable with.
Where Modbox fits
Modbox's locking models are the Aerobox curbside (16- and 18-gauge galvannealed steel, 16-gauge stainless adjustable latch with four openings: ½", 1", 1½" and 2") and the Courier wall-mounted (20-gauge with a 16-gauge housing wrap and the same stainless latch). Both can be left unlocked if you like the design but don't need the security, and the Aerobox's flag stows inside the body. Confirm the slot width on the product page against USPS's 1¾" × 10" guidance if you intend to run the smaller openings.
Frequently asked questions
Does the mail carrier have a key to my locking mailbox? No. Carriers deliver through the slot; only you open the compartment.
Can I put outgoing mail in a locking mailbox? Generally not; the carrier can't reach it. Use a separate slot, a collection box, or hand it to the carrier.
Are locking mailboxes USPS approved? Some are, under the Locked Mail Slot and Locked Large Capacity categories of USPS-STD-7C. Others are acceptable at the local postmaster's discretion. A slot at least 1¾" × 10" is the key requirement.
Do locking mailboxes stop package theft? Only if the box is a parcel locker. A standard locking mailbox protects letters and flats; packages still go to the porch.
Sources
- USPS-STD-7C, Standard Mailboxes, Curbside — https://about.usps.com/publications/engineering-standards-specifications/spusps-std-7c.pdf
- USPS, "How to Install a Mailbox" — https://www.usps.com/manage/mailboxes.htm
- USPS / Postal Inspection Service, mail theft prevention measures (May 2023) — https://about.usps.com/newsroom/national-releases/2023/0512-usps-postal-inspection-service-roll-out-expanded-measures-to-crack-down-on-mail-theft.htm