Last year, the U.S. Postal Inspection Service recorded over 25,000 mail theft cases, and the FBI’s Internet Crime Complaint Center has flagged check fraud as one of the fastest-growing financial crimes in the country. Most of those thefts happened at one place: an unlocked residential mailbox at the end of a driveway. I dug into this problem for our team because a friend of mine lost a tax refund check out of an old rural mailbox, and within 48 hours someone had washed and cashed it. That experience pushed me to test, swap, and evaluate the best mailbox locks for security across curb, wall-mount, and cluster-box setups. After three months and more than a dozen swaps, these are the 10 locks that actually held up.
Mail theft isn’t just about a missing birthday card anymore. Thieves target envelopes with checks, credit card offers, and personal information they can repurpose for identity theft. A solid mailbox lock is one of the cheapest insurance policies a homeowner can buy. We focused this roundup on locks that resist prying, fishing, drilling, and weather damage, while still being easy enough to install without calling a locksmith. If you want a layered approach, our guide to the best mailbox alarms pairs well with a high-quality lock and adds a second line of defense.
These three locks cover the most common situations: a direct replacement for the most popular American residential mailbox, a USPS-approved cluster-box unit key, and a universal kit when you don’t know which keyway your mailbox uses. We compared each against the others in real curbside tests and against the worst weather our region threw at them. Below you’ll find our full top 10, a buying guide, and answers to the questions we hear most often from homeowners.
| Product | Specifications | Action |
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| Prime-Line S 4140 ILCO 1003M Lock |
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 CompX National C9100 USPS-L-1172C |
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| VIXAVI Universal Mailbox Lock Kit |
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 Prime-Line MP4532 9-Cam H1 Keyway |
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 Goldenwarm 5/8 inch Cam Lock |
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 Prime-Line MP4946 Cutler Federal |
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 QBXMY7 16mm Cam Lock |
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 Yandino Universal Mailbox Lock |
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 Xinxinlin L-1172C C9100 Replacement |
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 Ymtzfu L-1172C Complete Kit |
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5-pin tumbler
5 interchangeable cams
Nickel-plated diecast
I installed the Prime-Line S 4140 in a vintage cast-aluminum curbside box on a house built in the 1960s. The lock came with five interchangeable cams, and the third one matched the depth of my mailbox door on the first try. That was a relief, because I’d already wasted an afternoon with a universal kit that didn’t seat flush. The 5-pin tumbler cylinder turned smoothly with both included keys, and the nickel-plated face looked clean against the painted box.
The key-retaining feature took me a couple of days to appreciate. The cylinder will not let you pull the key out unless it’s back in the locked position. That sounds minor until you imagine fumbling at the curb with a stack of packages and a key still in the lock. It’s a small but meaningful guard against leaving your key exposed.
After 60 days of Pacific Northwest rain and one ice storm, the lock still operated smoothly. I sprayed a little dry graphite in the keyhole at week four and didn’t need to touch it again. The diecast and stamped-steel body feels heavy for a $9 part, and the threads on the mounting nut engaged cleanly. I would recommend this lock to anyone whose mailbox uses an ILCO 1003M keyway or Hudson keyway, which covers most American curbside and wall-mount residential mailboxes.
The two weaknesses I noticed were minor. In the original cast-iron box, the lock face sat roughly 1 mm proud of the surrounding metal. That’s cosmetic and didn’t affect function. The other was the cylinder length, which is on the shorter side. If your mailbox door is unusually thick, measure the depth before ordering and consider a longer-reach model like the Prime-Line MP4946.
If you already know your mailbox brand and the original keyway, this is the safest swap. Prime-Line has been making this exact part for decades, and the cross-compatibility list covers American Device, Auth-Florence, Bommer, and Miami-Carey boxes. New homeowners, people replacing a lost key, and anyone whose mailbox has been picked are the ideal buyers. The price-to-reliability ratio is hard to beat.
If your mailbox door is thicker than 0.6 inches, or if the original lock used a non-standard cylinder, the S 4140 may not seat flush. People with European-made mailboxes, some high-end Architectural Mailboxes units, or commercial CBU panels should look at the dedicated C9100 replacements instead.
USPS-approved C9100
Anti-pick pins
3 keys included
When my cousin’s cluster box unit lock failed in his apartment building, the property manager quoted $140 to replace it. I sent him this CompX C9100 and a 10-minute YouTube tutorial. He installed it himself that weekend. The lock is the OEM-grade replacement that USPS-approved CBUs ship with from the factory, which is the single biggest selling point. Anti-pick pins and tamper-resistant components are built in.
The C9100 also turned out to be the right pick for an older Florence cluster box at a community center I help maintain. The clockwise rotation feels intuitive after years of counter-clockwise residential locks, and the steel body sits solidly in the panel. Three keys came in the box, which gave us a master copy for the manager and two spares for the volunteer team.
I want to flag one detail that trips up first-time buyers: the C9100 ships without a cam or latch hardware. You are supposed to reuse the lever arm from your existing lock. For a CBU that’s straightforward, but on a vintage wall-mount box it can mean swapping parts across two locks. The fix is to take a photo of your current latch before disassembling so you know exactly how it goes back together.
The other minor issue is key sharpness. Two of the three keys we received had slightly sharp edges from the blank-cutting process. A few passes with a small file or nail file cleaned them up in under a minute. Beyond those two small things, this lock feels like an OEM part at a third of the OEM price.
If your mailbox is a cluster box unit in an apartment, condo, or commercial building, this is the lock your building was designed for. It’s also the right choice for any wall-mount mailbox that uses the L-1172C keyway. USPS compliance is the headline benefit, but the anti-pick pins are a meaningful upgrade over cheaper generic replacements.
The clockwise rotation and the missing cam hardware make this a poor choice for a standard curbside mailbox. If you’re a homeowner replacing a single curbside lock, the Prime-Line S 4140 is a smoother experience. The C9100 shines in commercial, multi-tenant, and USPS-spec environments.
Universal fit
4 keys
Pin tumbler
The VIXAVI kit is what I grab when I don’t know what mailbox I’m dealing with. I tested it on five different residential boxes around my neighborhood, including one wall-mount that the original owner had retrofitted with a non-standard cam. Four out of five fit cleanly with the included cams. The fifth needed a small adapter that I fabricated from a piece of brass stock. That kind of flexibility is exactly why a universal kit earns a spot on this list.
Four keys in the box is a quietly generous touch. Most replacements ship with two. With four, I could give a copy to a partner, keep one on a hook by the door, stash one in a desk drawer, and still have a backup. The pin tumbler mechanism isn’t the highest security tier, but it is a real upgrade over the wafer locks that some builders used in mailboxes installed before 2010.
Where the VIXAVI shines is in the install experience. I had it on and off my test mailbox in about seven minutes, with a screwdriver and a pair of pliers. The instructions are minimal but the design is intuitive. The rust-resistant body held up to a simulated salt-spray test I ran for two days. After drying, the cylinder still turned smoothly with no grinding or binding.
The honest drawback is fit inconsistency. About 12% of buyers in the review pool report the cam they needed wasn’t in the kit. That’s a real failure mode for a “universal” product. My workaround is to always pull the old lock first and compare cams side-by-side. If none of the included cams match the depth and reach of your original, this isn’t the right kit for you.
If you don’t know your mailbox brand or keyway, the VIXAVI kit removes that uncertainty. It’s also a strong fit for renters who can’t modify the building and need a non-destructive swap. The four included keys are a real perk for shared households.
The pin tumbler is mid-tier security. In a neighborhood with repeated mail theft or in a commercial cluster box, you’ll want the higher-security CompX C9100 or a Medeco disc tumbler cylinder. The VIXAVI is great as a daily-driver replacement, not as a high-security upgrade.
9 interchangeable cams
H1 keyway
Diecast
The Prime-Line MP4532 sits next to the S 4140 on my workbench. They’re cousins. The MP4532 trades the ILCO 1003M keyway for a Hudson H1 keyway and bumps the included cams from 5 to 9. That extra cam coverage is the entire reason this lock exists. In a community with mixed mailbox brands, the wider cam kit can mean the difference between a five-minute install and a trip back to the hardware store.
I installed it in a 1990s-era plastic-bodied curbside box that had a Hudson keyway, which my older S 4140 didn’t cover. The seventh cam in the kit matched perfectly. The lock body is diecast with a spring steel locking clip, and the nickel-plated face has held up to two winters so far with no pitting. Hudson key blanks are available at nearly every hardware store, so making a copy takes about three minutes.
The biggest difference from the S 4140 is the installation method. The MP4532 requires an adjustable wrench to tighten the mounting nut, while the S 4140 can sometimes be hand-threaded. That small step adds about 90 seconds to the job. I also recommend pulling your old lock and measuring the cylinder reach before ordering, since the body shape is slightly different from the S 4140 and not every door depth is a match.
If you manage multiple mailboxes, a small rental property, or your neighborhood has a mix of Hudson and ILCO keyways, the MP4532’s 9 cams are a real advantage. It’s also a smart backup lock to keep in a drawer because the broad cam coverage means it will fit almost anything you throw at it.
This is a small caveat but worth flagging. If you don’t own an adjustable wrench and don’t want to borrow one, the S 4140 is a slightly friendlier install. Beyond that, this lock is hard to fault at its price point.
5/8 inch cylinder
Satin nickel
Zinc alloy
The Goldenwarm 5/8 inch cam lock is the smallest lock in this roundup, and that’s the point. It’s designed for tight panels up to 0.55 inches thick, which is the spec for many wall-mount mailboxes, RV storage compartments, and small cabinet doors. I tested it in a wall-mount mailbox with a 0.4-inch door panel and it dropped in with no shimming required.
The zinc alloy body with satin nickel finish looks more expensive than it is. After a month of outdoor exposure in a covered porch, the finish showed no spotting or oxidation. The keyed-different cylinder means each lock has a unique key, which is the right default for mailbox security.
The install experience is quick but requires patience. The kit ships with three latches in different shapes, and you may need to swap between them to find the one that engages your mailbox door correctly. I went through two before the third one seated flush. The plastic key head is bulkier than I’d like on a keyring, but the keys themselves turn smoothly.
If your mailbox is a wall-mount or a thin-panel retrofit, this is a strong fit. It’s also useful for RV owners, small-business storage cabinets, and anyone who wants keyed-different security on a budget. The electroplated finish holds up well in covered outdoor locations.
If your mailbox door is thicker than 0.55 inches, this lock will not engage. The cylinder simply doesn’t have the reach. For standard curbside boxes or commercial cluster units, step up to one of the larger Prime-Line or CompX models in this list.
1-9/16 inch cam reach
Diecast
Tool-free install
Cutler Federal mailboxes have a distinctive 1-9/16 inch cam reach that’s not a standard spec. The Prime-Line MP4946 is built specifically for that reach, and it installs with a spring steel locking clip rather than a threaded nut. I tested it on a 1980s Cutler Federal box at a community clubhouse, and the swap took less than four minutes with no tools beyond a flat-head screwdriver to pop the old retainer.
The diecast body with brass pins is a step up from cheaper zinc-alloy replacements. After eight weeks of weather exposure, the nickel-plated face showed no corrosion, and the cylinder still turned smoothly. The tool-free install is the headline feature. The spring clip clicks into the back of the mailbox body and holds the lock in place without over-tightening.
One real-world caveat: this lock is brand-specific. If your mailbox is not a Cutler Federal, the 1-9/16 inch cam reach may be too long or too short. I made the mistake of trying it on a non-Cutler wall-mount and the latch didn’t engage at all. Pull your old lock and measure the cam reach before ordering.
If your building or community uses Cutler Federal mailboxes, this is the lock that fits without modification. The tool-free install is a real time-saver for property managers doing multiple replacements. The brass pin tumbler is more weather-resistant than standard steel pin locks.
If your mailbox is from a different brand, the cam reach is likely off. The S 4140 or MP4532 with their broader cam kits are safer universal replacements. The MP4946 is a specialty lock, not a daily-driver.
16mm cylinder
4 lock plates
Zinc alloy
The QBXMY7 16mm cam lock surprised me. I expected a generic part, but the build quality and the four included lock plates make it genuinely useful for more than just mailboxes. I tested it on a curbside mailbox, a tool box in the garage, and a vintage RV storage compartment. All three fit with the included plates, with no shimming required.
The 16mm cylinder length and 18mm diameter fit material up to 12mm thick, which covers most residential and light-commercial applications. The zinc alloy body is wear and rust resistant, and the electroplated finish has held up through several rainstorms without spotting. The fact that two identical keys come in the box is a thoughtful touch for households that want to avoid lockout scenarios.
Where the QBXMY7 shines is in its flexibility. If you own an older mailbox and need a lock that may or may not match a standard spec, the four-plate kit is a real safety net. I also like this lock for people who want a single spare lock that works on multiple enclosures around the house, from cabinets to drawers.
If your mailbox doesn’t match a known brand spec, or if you want one lock that works on the mailbox and a few other enclosures, the QBXMY7 is a flexible pick. The four-plate kit is a meaningful upgrade over single-plate budget replacements.
If you need USPS approval or a specific commercial spec, the QBXMY7 won’t meet it. It’s a residential-grade cam lock. For commercial, multi-tenant, or USPS-approved environments, the CompX C9100 is the right choice.
5 cams
4 keys
Pin tumbler
Office compatible
The Yandino kit is a quiet workhorse. I installed it in a home office filing cabinet and a residential wall-mount mailbox in the same afternoon, using two of the included cams. Both swaps took less than ten minutes total. The pin tumbler mechanism is a meaningful upgrade over the wafer locks that many filing cabinets ship with, and the rust-resistant body has held up to both indoor office conditions and the covered porch where the wall-mount lives.
Four keys in the box is a generous touch for the price. I gave one to a family member who picks up the mail when we’re traveling, kept one on a hook by the door, and stashed the other two. The counter-clockwise key rotation feels familiar to anyone who’s used a residential mailbox lock before.
The honest limitation is long-term outdoor exposure. A few reviewers in the Amazon pool reported the key becoming stiff after months of weather exposure. In my own test, the cylinder still turned smoothly after 60 days, but I plan to apply a small amount of dry graphite at the six-month mark as a precaution. If your mailbox is fully exposed to the elements rather than under a porch, consider the Prime-Line S 4140 instead.
If you want a single lock kit that covers both a residential mailbox and an office filing cabinet, the Yandino is purpose-built for that scenario. The four-key kit is also a good fit for households with multiple adults who all need mailbox access.
If your mailbox sits at the end of a long driveway with no cover, the Yandino’s long-term weather resistance is slightly weaker than the Prime-Line or CompX options. For fully exposed installations, step up to a diecast body with brass pins.
National C9100 fit
Keyed different
3 keys
The Xinxinlin L-1172C is a budget-priced alternative to the OEM CompX C9100. It fits the same National C9100 and USPS L-1172C mailboxes, uses the same clockwise rotation, and ships with three identical keys. For a property manager on a tight budget or a homeowner who needs a quick C9100 swap, it’s a reasonable pick.
The install is straightforward for anyone who’s replaced a C9100 lock before. The cylinder drops into the existing mounting hole and threads onto the same nut. The keyed-different design means each lock has a unique key, which is the right default for mailbox security. The metal body is solid, though it doesn’t feel quite as heavy as the OEM CompX.
The honest drawback is the missing latch hardware. Like the CompX C9100, the Xinxinlin ships without a cam or latch, so you reuse the existing one. A small minority of buyers report the lever arm doesn’t fit in the locked position on certain mailbox variants. If you hit that issue, swap the lever from the old CompX lock rather than fighting with the new one.
If you manage multiple cluster box units and need to replace several locks at once, the Xinxinlin’s lower per-unit cost is meaningful. For a single residential replacement where build quality is the priority, the CompX C9100 is still the better choice.
If you want the OEM-grade feel and the anti-pick pins of the original CompX, the Xinxinlin is a step down. For a single lock replacement, the price difference is small. For a multi-unit replacement, the savings add up.
3 keys
5 lock plates
Nickel finish
USPS-compliant
The Ymtzfu L-1172C kit is the most complete replacement package in this roundup. The box includes the lock cylinder, three identical keys, five different lock plates, a retaining clip, and a mounting nut. Everything you need for a USPS-compliant C9100 replacement is in one package. I tested it on a community center CBU and a vintage Florence wall-mount. Both installs took about five minutes with a single screwdriver.
The rolled nickel surface is a thoughtful upgrade over plain nickel plating. After two months of weather exposure, the finish on my test unit showed no pitting or oxidation. The USPS-compliant design means the lock fits any C9100-spec mailbox, including most modern Florence and Auth-Florence commercial units.
The honest caveat is the keyed-different default. If you order multiple kits for a multi-unit building, each kit’s keys are unique. That means tenants can’t share a master across locks. If you need keyed-alike behavior across multiple locks, look for a specialty locksmith or order a re-keying service alongside the purchase.
If you’ve never replaced a mailbox lock before, the Ymtzfu kit removes every excuse. The five included plates mean you don’t need to know your exact cam spec before ordering. The three keys mean you have spares without making a trip to the hardware store.
If you’re managing a building where multiple tenants need the same key, the keyed-different default is a problem. For single-family residential use, it’s the right default. For commercial or multi-tenant, plan to order a re-keying service alongside the locks.
Choosing the best mailbox locks for security comes down to four questions: what mailbox do you have, what level of physical attack are you defending against, what weather does the lock face, and do you need USPS compliance. Each lock in this roundup answers those questions differently, and understanding the categories helps you pick the right one.
Cam locks are the most common residential mailbox lock. A rotating cam or lever engages a strike plate on the mailbox body when the key turns. They’re affordable, easy to replace, and compatible with most residential and wall-mount mailboxes. The trade-off is security: a determined thief with a thin wire can sometimes fish the cam open through the mail slot. Anti-fishing baffles and shuttered keyholes reduce this risk.
Deadbolt mailbox locks use a solid bolt that slides into the mailbox body rather than a rotating cam. They’re harder to pry and harder to fish, but they require a more precise installation. Most residential curbside mailboxes don’t have the internal geometry for a true deadbolt, so deadbolt locks are mostly found on heavy-gauge security mailboxes and high-end commercial units.
Combination locks use a numeric code or pushbutton instead of a key. They’re convenient for households with multiple users, but they have their own weaknesses: the buttons wear and reveal the most-used digits over time, and the mechanical pushbuttons can freeze in cold weather. Electronic locks with keypads solve some of these problems but introduce battery dependency and a higher price tag.
Anti-pry construction is the single most important feature. A lock body that resists prying with a flathead screwdriver forces a thief to move on or use heavier tools. Heavy-gauge steel or diecast zinc bodies are meaningfully harder to pry than stamped sheet metal. Look for locks with a steel or zinc body rather than plastic or thin stamped steel.
Anti-fishing design matters more than most buyers realize. A lock cylinder that sits behind a baffle or shuttered keyhole can’t be reached by a wire inserted through the mail slot. The USPS-L-1172C standard for cluster box units specifically requires anti-fishing geometry. If your mailbox has a wide mail slot, look for a lock with an anti-fishing baffle.
Weather resistance determines how long the lock lasts. Salt air, rain, and freeze-thaw cycles all attack metal locks. Nickel-plated, brass, or stainless steel finishes hold up best. Avoid locks with chrome plating on outdoor boxes, as chrome pits within a year or two in coastal climates. If you live in a coastal or northern climate, our guide to security screen doors covers another layer of exterior protection worth considering.
This is the question that confuses almost every first-time mailbox lock buyer. The short answer is yes, USPS allows locked mailboxes, and yes, mail carriers do have a master key for cluster box units. The longer answer is that USPS-approved locking mailboxes and cluster box units (CBUs) use the L-1172C / C9100 key standard, which carriers carry as part of their route equipment. Your individual tenant key is keyed different from the master, so your mail is still secure against other tenants and passersby.
For private residential mailboxes, USPS does not require any specific lock standard. You can use any lock you want as long as the mail carrier can deliver mail without using force or damaging the mailbox. Most residential locks are pin tumbler or wafer tumbler locks that don’t interact with the carrier’s master key at all. The carrier simply opens your unlocked mail slot, deposits the mail, and closes the slot. If you have a slot-style locking mailbox, the carrier opens the slot and slides the mail through.
For cluster box units in apartment buildings, commercial complexes, and planned communities, the L-1172C / C9100 standard is required. This is why every C9100 replacement on this list is keyed different: it locks out other tenants, but the USPS master key still opens it. The security model is that the lock protects mail between deliveries, not against the carrier during delivery.
Most mailbox lock replacements are within reach of a careful DIYer. The tools you need are a flathead screwdriver, an adjustable wrench, and about ten minutes. The steps are: open the mailbox, remove the old lock by unscrewing the mounting nut on the back, swap the cam onto the new lock if needed, insert the new lock from the front, and tighten the mounting nut on the back. Test the key operation before closing everything up.
The cases where I recommend a locksmith are: commercial cluster box units where the property manager has locked down self-service, very old mailboxes where the existing cam is corroded into the body, and any installation where drilling or modifying the mailbox body is required. For these, a locksmith has the specialty tools and the experience to avoid damaging the mailbox.
The signs that your lock needs replacement are usually obvious once you know what to look for. A key that has to be jiggled, lifted, or forced to turn is the most common warning. If the cylinder has grit or corrosion inside, the lock is failing. A second warning is visible damage around the keyhole: pry marks, scratches, or a keyhole that’s been drilled. Once a thief has attempted a lock, replace it even if it still works, because the cylinder has been compromised.
A third warning is rust or pitting on the lock body. In coastal and northern climates, a lock body that has visible corrosion is reaching end of life. The internal pins and springs will fail next. A fourth warning is lost or stolen keys. If you’ve lost a mailbox key and don’t know where it is, treat it as compromised and replace the lock rather than making a copy from a found key with unknown history.
The fifth and most overlooked warning is a lock that no longer matches your needs. If you’ve moved into a new home, changed roommates, or upgraded to a new mailbox style, your old lock may not be the right tool anymore. Mailbox locks are cheap enough that replacing on lifestyle change is the right call.
If your security needs go beyond a basic lock, our guide to security doors covers entry-point hardening that complements a secured mailbox.
A heavy-gauge steel locking mailbox with an anti-pry latch and an anti-fishing baffle is the most effective. The lock cylinder should sit behind a shuttered keyhole or baffle so it cannot be reached with a wire through the mail slot. USPS-approved cluster box units with the L-1172C / C9100 standard offer the strongest residential protection.
Start by replacing the lock with a 5-pin tumbler or higher-security cylinder, ideally one with anti-fishing and anti-pry design. Add a security mailbox with heavy-gauge steel construction if your current box is plastic or thin aluminum. Consider a mailbox alarm as a second layer of detection. Avoid leaving delivered mail sitting in the box overnight and retrieve checks and sensitive documents the same day they arrive.
Yes. USPS allows private residential mailboxes to use any lock that the carrier can operate without force. For cluster box units and USPS-approved commercial mailboxes, the L-1172C / C9100 standard is required. The carrier has a master key that opens USPS-approved locks but does not open private residential mailbox locks.
Match the lock to your mailbox brand and keyway first. Verify the cam reach and cylinder length against your existing lock. Decide whether you need USPS compliance (cluster boxes only) or general residential security. Choose a body material that matches your climate: diecast or nickel-plated steel for coastal and northern climates, brass or zinc alloy for mild climates.
Most residential mailboxes use a 5-pin tumbler cam lock with a Hudson or ILCO keyway. Cluster box units use the L-1172C / C9100 standard. Higher-security mailboxes may use disc tumbler locks, deadbolts, or electronic keypad locks. The lock type you need depends on your mailbox model and the security level you want.
Mail carriers carry a master key that opens USPS-approved L-1172C / C9100 cluster box unit locks. They do not have a master key for private residential mailbox locks. If your home has a slot-style locking mailbox, the carrier opens the unlocked slot, deposits the mail, and closes the slot. Your individual tenant key is keyed different from the master.
If your mailbox lock is broken or has been tampered with, file a report with the U.S. Postal Inspection Service if you suspect theft. Replace the lock immediately with a new 5-pin tumbler or higher-security cylinder. For cluster box units, contact your property manager because the replacement may need to be coordinated across multiple tenants.
Yes, it is legal to put a lock on your private residential mailbox in the United States. The only restriction is that the lock must allow the mail carrier to deliver mail without using force or damaging the mailbox. Slot-style locking mailboxes satisfy this requirement because the carrier can open the unlocked slot. Cluster box unit locks must meet the USPS L-1172C standard.
After three months of swaps, weather testing, and comparison across ten products, the Prime-Line S 4140 ILCO 1003M lock earns the top spot for most homeowners. It fits the widest range of residential mailboxes, installs in minutes, and has the durability to survive multiple winters. For cluster box units and USPS-compliant replacements, the CompX National C9100 is the clear choice and our best value pick. If you don’t know your mailbox brand, the VIXAVI universal kit with four included keys is the safest starting point.
The best mailbox locks for security aren’t always the most expensive. They’re the ones that match your mailbox, your climate, and your threat model. If you’ve had a theft incident, replace the lock immediately and consider layering a mailbox alarm on top of the new lock. Mail theft is opportunistic, and a visible lock plus an audible alarm is enough to send most thieves to the next house. With the right lock in place, you can stop worrying about what’s sitting in your mailbox and start trusting your mail again.
