To replace the lock on a mailbox you own, open the door, unscrew the cam, remove the retaining clip or nut, slide the old cylinder out and install a new one with the same barrel diameter, cam and turning direction. On most boxes it is a short job with a screwdriver. Locks on USPS-owned cluster boxes are changed only by the Post Office, and locks on HOA or apartment mailboxes by management.
This guide covers which locks you are allowed to change, the main lock types, how to measure for a replacement, the step-by-step swap, and what managers of cluster and 4C mailbox locks and key blanks need to know. If you only need a key, see our guide on how to get a new mailbox key.
Before you start: can you change this lock?
Ownership decides it. USPS rules make customers responsible for the receptacles they buy, while USPS provides lock and key service on the cluster box units (CBUs) it owns, and property owners provide it on private ones (Postal Operations Manual 632.22).
| Mailbox | Who changes the lock |
|---|---|
| Locking curbside, wall-mount or column mailbox you own | You or a locksmith |
| USPS-owned cluster box unit | Your local Post Office. If all keys are lost, USPS installs a new lock and keys at the customer's expense. |
| HOA or developer-owned cluster box | The HOA, builder or property owner |
| Apartment 4C or 4B mailboxes | Building owner or manager |
| The carrier's master door on any cluster or apartment unit | USPS only. Never remove or alter it. |
If you rent or live in an HOA, ask before you touch anything. Swapping a tenant lock on a unit you do not own can lock management out of a compartment it is responsible for.
Find your key number first
Replacement keys are one of the most common things customers email us about after a sale, and the answer usually depends on one thing: the code stamped on the key.
- You have the code: order duplicates from the manufacturer. We cannot supply Mail Boss or Jayco keys.
- You lost every key and the code: replace the lock. Mail Boss keeps no record of key numbers, there is no universal key, and we cannot look up a code from your order.
- A locksmith cannot help: one customer's locksmith could not copy their key, so try the manufacturer first.
- The lock is jammed or broken: the old lock has to come out first, usually by drilling it out.
This comes up a lot with rentals. When a tenant leaves without returning keys and yours are gone too, a new lock is the only option.
Replace or rekey?
- Replace means a new lock cylinder with new keys. It is the usual DIY route on residential mailboxes because replacement cylinders are inexpensive and come with keys.
- Rekey means keeping the cylinder and changing its internal pins or wafers so a new key works and old ones do not. It is usually a locksmith job, and not every mailbox lock can be rekeyed.
Either one locks out old keys. If you just bought a house, had keys stolen, or noticed mail going missing, do one or the other rather than just cutting a copy.
Types of mailbox locks
| Lock type | Where you see it | Notes |
|---|---|---|
| Cam lock (pin or wafer) | Most residential locking mailboxes, older apartment boxes | A key turns the cylinder, which rotates a flat metal cam behind the door. Generic replacements are widely sold. |
| High-security disc wafer lock | Mail Boss locking mailboxes | Mail Boss uses a commercial-grade 12-disc wafer lock. The manufacturer sells replacements matched to each model, with the correct cam. |
| 5-pin cylinder with hook cam | Jayco Letter Lockers (Level 1) | Jayco's standard lock is a 5-pin cylinder with a stainless steel hook cam. |
| Medeco deadbolt | Jayco Letter Lockers (Level 2 and 4 options) | A high-security upgrade usually serviced through the manufacturer or a Medeco-authorized locksmith. |
| Tenant compartment lock | Cluster box units and 4C apartment mailboxes | Manufacturer-specific. Order replacements from the mailbox maker, matched to the unit. |
Combination locks show up on some residential boxes, but USPS does not approve them for apartment receptacles (POM 632.625).
How to measure for a replacement mailbox lock
The safest way is to take the old lock with you or photograph it next to a ruler. If you are buying a generic lock, check five things:
- Barrel diameter. The outside diameter of the cylinder, which matches the hole in the door. Common residential sizes include 3/4 in. and 7/8 in.
- Cylinder length. How far the lock reaches through the door. It must clear the door thickness and leave room for the clip and cam.
- Cam length and shape. Measure from the center of the cylinder to the tip of the cam, and note whether it is straight, bent or offset. The cam has to reach behind the frame far enough to hold the door shut. Many universal locks include several cams.
- Turning direction. Note whether the key opens the lock clockwise or counterclockwise, and how far it turns (often a quarter turn).
- How it is held in. A spring clip, a hex nut or a screw-on retainer. Your new lock should use the same method, or come with what you need.
If your mailbox is a branded model, start with the manufacturer. Mail Boss, for example, sells a replacement lock with three keys and the cam for your specific model, and tells you to check the silver tag inside the upper (non-locking) door for the model name.
How to change a mailbox lock: step by step
These steps fit most residential locking mailboxes with a cam lock. Tools: a screwdriver, needle-nose pliers, and a wrench if the lock uses a nut.
- Confirm you own the mailbox. See the table above. On a cluster or apartment box, stop here and contact the Post Office or management.
- Open the door. Use your key. If no key exists, a locksmith can open it, or you can drill out the lock on your own box. Our guide on how to drill out a mailbox lock explains how.
- Note the cam position. With the door open and the lock in the locked position, take a photo of how the cam sits. You will copy this on the new lock.
- Remove the cam. Unscrew the screw or nut on the back of the cylinder and lift the cam off.
- Remove the retainer. Slide off the spring clip with pliers, or unscrew the retaining nut.
- Push the cylinder out through the front of the door.
- Insert the new cylinder from the front, oriented the same way as the old one (keyway up or down as before).
- Fit the retainer so the cylinder cannot spin or pull out.
- Attach the cam in the same position as your photo, with the screw snug.
- Test with the door open, then closed. The key should turn smoothly, the cam should catch firmly behind the frame, and the door should not pull open when locked.
- Store a spare key away from your key ring and write down the key number.
Changing locks on cluster boxes and 4C mailboxes
USPS-owned cluster boxes
Residents do not change these locks. The Post Office provides each customer a compartment lock and three keys, keeps no duplicates, and installs a new lock and keys at the customer's expense if all keys are lost. Residents may copy their keys at their own expense. The USPS FAQ says there is no set fee for a lock change; it is based on local costs.
HOA, apartment and other private units
On privately owned CBUs and 4C horizontal mailboxes, the owner or manager provides lock and key service. Tenant locks are specific to the manufacturer, so order replacements matched to the maker of your unit. For Salsbury 4C horizontal mailboxes, see our 4C locks and key blanks (standard tenant locks, parcel locker locks and key blanks), or contact us with the brand and model of your unit.
USPS rules for apartment mailboxes (POM 632.625 and 632.627) add a few points managers should follow:
- Do not put key numbers on the outside of the lock barrels, and keep key records.
- Masterkeying tenant locks is not permitted.
- The carrier's master lock (the Arrow lock, which USPS is replacing with electronic locks in some areas) belongs to USPS. When an inside Arrow lock is no longer needed, management must notify the postmaster, and repairs are made only with a postal representative present.
- Receptacles must be kept locked and in good repair, or delivery can be withheld after written notice.
Replacing a whole bank of worn or damaged units instead? Our guide to HOA cluster mailbox replacement walks through who pays and how postmaster approval works.
Can I add a lock to my regular mailbox?
No. The curbside mailbox standard, USPS-STD-7C, prohibits locks on mailbox designs that are not approved as locking designs, and the POM prohibits locks, locking devices or inserts on curbside mailboxes on rural and highway contract routes, pointing customers to approved locking-style mailboxes instead. Carriers do not open locked boxes or accept keys.
The legal way to lock your mail up is a mailbox built as a locking design, with a mail slot or hopper the carrier can use without a key. Browse our locking mailboxes, or read our locking mailbox buying guide to compare models.
When a new mailbox beats a new lock
A fresh cylinder does not help if the door is bent, the hinges are loose or the box can be pried open. Consider replacing the mailbox if:
- The box is plastic or thin sheet metal and has been forced before.
- Rust has weakened the door frame around the lock.
- There is no anti-pry latch, so a screwdriver in the door gap can defeat any lock.
The Mail Boss Mail Manager is a common upgrade: 14 and 16 gauge electro-galvanized steel, a 12-disc high-security wafer lock with 3 keys, and a patented anti-pry latch. Our guide to preventing mail theft covers the habits that matter as much as the hardware.
Mailbox lock questions
Does the rear door use a different key?
No. On rear-access Mail Boss boxes, the rear lock opens with the same key as the front.
Can I replace the lock on my cluster mailbox myself?
Not if USPS owns it: the Post Office handles those locks. On an HOA or apartment unit, ask management, which is responsible for lock service. You can only swap locks yourself on a mailbox you own.
What size lock do I need for my mailbox?
Match the barrel diameter (often 3/4 in. or 7/8 in.), cylinder length, cam length and shape, and turning direction. Taking the old lock to the store, or ordering from the mailbox maker, avoids mistakes.
How do I change a Mail Boss mailbox lock?
Mail Boss sells a replacement lock with three keys and the cam for your model. Check the silver tag inside the upper door for the model name, then remove the cam and retainer and swap the cylinder.
Can a mailbox lock be rekeyed?
Many pin and wafer cylinders can be rekeyed by a locksmith, which keeps the lock and changes the key. On residential boxes a new cylinder is often just as easy. Either way, old keys stop working.
Can I put a padlock on my mailbox?
No. USPS standards prohibit locks on mailboxes not approved as locking designs, and carriers will not use keys. Buy a USPS-approved locking mailbox with a slot or hopper instead.
Shop locks and locking mailboxes
Browse 4C horizontal locks and key blanks for commercial units, or locking mailboxes for your home. Not sure which lock fits your box? Contact us with the brand and a photo.
******It is always recommended to contact your local postmaster prior to installation. While most of our mailboxes are USPS-approved your local postmaster may have specific preferences in terms of mailbox types and installation location******