WHAT IS THIS? THIS IS A MAIL RELAY.

You might have seen one of these green boxes sitting on a street corner. Maybe you were looking for a mailbox and thought you’d found one. But even though they look like normal mailboxes, there’s no slot for you to put mail in. That’s because they aren’t mailboxes at all, at least not in the usual sense. These are mail relay boxes.

You can usually spot them by their green color, as opposed to the deep blue of standard mailboxes. Relay boxes are used by the United States Postal Service as temporary storage while mail is out for delivery. This is especially important in a place like New York City where many postal workers still deliver on foot.

A Mail Relay Covered in Graffiti — Mail relays are frequent targets of graffiti and stickers.

Here’s how the system works. One postal worker brings mail to the relay box, often by truck. Another worker picks it up from there and delivers it to nearby addresses. That way, carriers don’t have to haul everything at once and they don’t need to return to a post office every time they need more mail. And that matters because New York City has over 10,000 relay boxes, compared to only about 230 post offices.

Three Mail Relays — Mail relays are often clustered together, like this group of 3 in front of the NYPL.

Many of these relay boxes were installed in the 1950s when mail volume was growing rapidly year over year. But that growth didn’t last forever. Mail volume peaked in the early 2000s. By 2024, the Postal Service was handling just over half as many pieces of mail as it did in 2000.

So while relay boxes are still a quiet but essential piece of the city’s mail infrastructure, the question is will they always be?