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boredzo
@boredzo

You've probably seen an arrangement like this at certain shopping centers (this one's near a grocery store), or you might even have or have had one where you live. What is it? And why is that key in the lower-right just hanging there?

Each of these things is a collection of mailboxes called a cluster box unit. There are three CBUs in this photo, and they have a couple of neat features that I want to highlight.


Each of the numbered compartments is one tenant's mailbox. They receive all their regular mail—bills, statements, circulars, you know—in their mailbox, to which they have a permanent key for the duration of their tenancy. Mail is delivered not directly to their door, but in their numbered box in their CBU. The local Post Office knows which box goes to which tenant's address.

The drop slot halfway up the right half of each CBU is for outgoing mail. If a tenant (or, really, anyone if they feel bold enough) wants to mail out a vaguely letter-sized mailpiece, as long as it will fit through that slot, they can slip it in there rather than have to find a Collection Box (blue freestanding mailbox) or go to a Post Office.

The real interesting bit, though, is those two large compartments at the bottom.

Those are called parcel lockers. As the name implies, they're for receiving packages rather than letters. They're a shared resource; any tenant may receive a package in any parcel locker. And the way they're allocated and secured is clever as hell.

You'll notice that one of the parcel lockers has a key hanging in the lock. What's up with that? And how do I know that it's empty?

If you look closer, you'll see that each parcel locker has two keyholes. One is for the postal carrier, and the other for the tenant/recipient. The recipient keyhole is the one the key is hanging in.

If you were to walk up to that CBU on the right and try to pull the key out, you'll find that you can't. If you manage it, congratulations on becoming the new King of England; you'll need the diplomatic immunity when the USPS comes for you.

What about the other parcel lockers—where are their keys? Those keys are sitting in some of the tenants' mailboxes, likely on top of that day's mail.

See, the way a parcel locker works is, when the postal carrier shows up with your package, they open the whole CBU at once (the whole front just swings open), then put the package in, then use their key to allow them to pull out the recipient key for that locker so they can put it into the recipient's mailbox.

[I've edited that last paragraph; I had previously asserted that the postal carrier used their key to unlock and open the parcel locker specifically. I know postal carriers open the whole CBU at once, so unlocking specific boxes doesn't make sense—upon considering that, I think the second keyhole is just for freeing the recipient key.]

When the recipient arrives to collect their mail, they'll find that on top of their bills, statements, circulars, etc. is a key. The key probably has a tag that indicates which parcel locker it belongs to (you can see such a tag hanging from the key in the photo).

The recipient finds the parcel locker indicated by the tag, unlocks it with the recipient key, and retrieves their package. They can close the door, but—just like you—they can't pull the key out again without the postal carrier's key. It's meant to stay there, until the next time the postal carrier has a package for someone.

So the parcel locker in the photo that has a key hanging from it is empty. I know that because if it had a package in it, the key would be in someone's mailbox, waiting for them to collect the key and in turn their package. That's the state of the other lockers: each of those has a package in it, and its key is waiting in some tenant's mailbox for retrieval.


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in reply to @boredzo's post:

Nope. One thing I didn't mention is that a parcel locker with a key in its keyhole is unlocked. Normally there's no use for this information because the locker is empty. But if you retrieved one package but there's another still inside, the key is still in the keyhole and turning it will reopen the door, so you can grab your second package.

(And it'll probably still be there, because there's no reason for a thief to suspect that an unlocked parcel locker with a key in its keyhole has a package in it.)

The locker won't lock again until the postal carrier next puts a package into it and takes out the recipient key.

in the parcel lockers i've used the key locks in the open position. that's part of the mechanism that locks the key in place. if the door swung shut, it wouldn't matter because there's no active latching mechanism until the postal worker removes the resident key.

I have one of these even though I'm a homeowner, they installed it on the side street near my house way back before I bought this house because the road is dangerous and the USPS truck got rear-ended more than once by someone blowing around the low-visibility curve way too fast.

one of the more interesting conversations i've had recently was asking my building's letter carrier if the mailbox situation was as terrible for him as it seemed (individual boxes mounted in, like, bizarrely inaccessible places). dude had some THOUGHTS.

yet another one of the myriad of ways landlords are terrible is by failing our postal workers with cheap and awful mailboxes.

I lived in a big apartment complex where this happened pretty regularly. For residents there, it meant your delivery was delayed a day or so. I'm not sure I'd this is the standard practice everywhere, though, since I used to live in a town where you'd get a notice that a package was available for pickup at the usps office if they couldn't fit the package in your mailbox.

That's one of the possible causes of redelivery, for which there are a few options.

Depending on package and the sort of address being delivered to, the postal carrier might deliver one or more of the parcels directly to the address (i.e., on someone's doorstep or at a business's front desk). Another option is that the package may be held at the local Post Office; the postal carrier will write up a slip telling you where you can get your package, and put that in your mailbox.

I think in some circumstances they might also just try again the next day. You might get a redelivery notice that says it was the first attempt, but you might not need to do anything.

These are also the remedies if a package is too big to fit in any available parcel locker.

I used to have one of these in a subdivision I lived in, where all the houses on 2-3 streets would go to the same mailbox unit for their mail. If there were a lot of packages (as there often were this time of year) they would deliver them directly to the houses.

Also, if the packages were small enough, they'd just shove them in the letter boxes too instead of using the lockers. Ours were shaped more like a half gallon milk carton laying on its side than the thin rectangle slots pictured in this post, though.

I live in a house next to a small apartment, and have one of these instead of a typical mailbox. I honestly prefer it - my neighborhood gets a lot of packages stolen off porches, and this just means one less headache for me.

I receive my mail in one of these units, but packages are usually just delivered to my door instead. There's not enough parcel lockers, and they're not large enough to accept a lot of items. In 4 years at this address, I think I've received a parcel in the parcel locker three times. And in one case, the carrier wedged a parcel in so tightly that there was no room for the key to turn, and they delivered it to my door the next day.

They made a change last year in response to this exact problem (the scarcity, not the size issues), but only for wall-mounted receptacles in apartment buildings.

The old standard for apartment buildings was 10:1: for every ten assigned mailboxes, there had to be at least one parcel locker. Now it's 5:1.

Of course, it doesn't immediately help anyone in an existing building that was set up to the 10:1 standard; the requirement applies to “all new and remodeled apartment buildings”.

I don't know whether there's any such ratio requirement for CBUs. The wall-mounted receptacle standard is standard 4C; the specification that covers CBUs is apparently “USPS-B-1118” but I can't find a copy of that online.

posts like this are why im on cohost. an article about the ridiculously clever mailbox design would never pop into my feed on any other platform. good thread, thanks for writing it up!

I dislike these things. I've always lived places where the mail is delivered to my door and parcels left at a nearby drugstore or corner shop but I've used one of these central lockers for my parents. They mainly seem like a way to reduce the service provided by the national mail and wages and jobs available for postal workers and local small businesses.

my apartment complex (in the US) has one of these. i thought the parcel locker was a fun idea when i moved in too. there's something delightful about unlocking a mailbox and finding another key inside. the locker key makes a very satisfying ratcheting clicking noise when you insert it.

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