The Psychology of Postcrossing: Why Hundreds of Thousands of People Mail Postcards to Strangers
On variable rewards, childhood penpals, and the delight of mail you never saw coming.
By Katie Blake, PhD | Social & Cultural Psychologist
When I was a kid, I went to camp one summer and came home with a penpal. I don't remember much about how it started — a piece of paper passed between bunks, probably, or an address scrawled on the back of something else — but I remember what it felt like over the months that followed. Checking the mailbox before anyone asked me to. The recognizable shape of an envelope that wasn't a bill or a flyer. The fact that someone I'd known for two weeks in July was still, somehow, a part of my life in October, one letter at a time.
I hadn't thought about that penpal in years until I came across Postcrossing — an online project where members are matched at random to send each other postcards, with no other relationship attached. You sign up, you're given a stranger's address somewhere in the world, you send them a postcard, and at some unknown point later, a stranger somewhere else sends one to you. There are more than 800,000 people doing this, in over 200 countries, and they've exchanged something like 85 million postcards. It is, on paper, a strange thing to be popular: paying for a stamp to mail something you made an effort over to someone you will probably never speak to again.
And yet I understand it completely, because I felt a smaller version of the exact same thing more recently, at a retreat. On the first night, we were each handed a piece of paper and asked to write a letter to ourselves — whatever was true at that moment, however unfinished. The organizers collected them, said nothing else about it, and that was that. I forgot about it almost immediately. Weeks later, a letter showed up in my mailbox in my own handwriting, and I had no complete memory of what I'd written until I opened it. I sat down with a cup of tea to read my own words back to myself like they belonged to someone else, and felt something I can only describe as delighted.
I think that delight is the actual subject here. Not postcards specifically. The palpable pleasure of not knowing when something good is coming.
Why Not Knowing Is What Keeps You Coming Back
There's a well-established finding in psychology, going back to B.F. Skinner's research on reinforcement, that rewards delivered on an unpredictable schedule create a stronger pull than rewards you can count on. If you know exactly when something good will happen, you anticipate it and then it's over. If you have no idea when it will happen — only that it will, eventually — you stay engaged in a low buzz of anticipation that a guaranteed reward never produces.
This is, uncomfortably, the same mechanism behind a slot machine. It's the same mechanism behind checking your phone for a notification that might not be there. Variable, unpredictable rewards are subtly one of the most reliable ways to keep a person coming back to something, which is exactly why so much of the modern attention economy is built around them.
What I find genuinely interesting about Postcrossing is that it runs on the identical psychological wiring — and channels it toward something almost entirely wholesome. You send a postcard into the world with no idea who will get it. You have no idea when your own postcard will arrive, or from where, or what it will say. The system is engineered around not-knowing in exactly the way a slot machine is, except what's waiting on the other side is a handwritten note from a stranger in Taiwan or Estonia, not a small loss disguised as a near-win. Same mechanism. Completely different use.
There's a second layer to why this particular kind of not-knowing feels good rather than anxious: the reward, when it does come, is low-stakes and inherently kind. Nobody sends a Postcrossing postcard to criticize you. The worst-case outcome of waiting is mild disappointment, not real harm. That combination — genuine unpredictability with no downside — is rare, and it might be part of why people stay in this hobby for years, the way some Postcrossing veterans openly say they have.
The Stranger Part Isn't a Bug
It would be easy to assume the appeal is really about international postcards specifically — pretty stamps, exotic postmarks, a card from a country you've never visited. That's part of it. But I think the deeper appeal is that the sender is a stranger.
A postcard from a friend is lovely, but it's also expected, in the sense that you already know roughly what they might say and how they'd say it. A postcard from someone whose name you've never heard, who lives somewhere you may never go, who chose this specific card and these specific words for a person they know nothing about except a randomly assigned address — that's a small act of effort with no relationship obligating it. Nobody owes you that postcard. They sent it anyway, to a name they'll likely never think about again.
There's something in that which echoes a finding from belongingness research: humans don't only need close relationships to feel okay — we also benefit from small, low-stakes interactions with people outside our existing circle. A stranger's brief kindness can register, psychologically, as its own kind of connection, distinct from but not lesser than the deep kind. Postcrossing seems to have built an entire infrastructure around exactly that flavor of connection — wide instead of deep, brief instead of ongoing, and oddly sustaining anyway.
It's also, practically, a low-cost hobby by design. Most experienced Postcrossing members will tell you the same thing: postcards are simple and affordable. Unlike other hobbies, this one requires relatively little financial commitment and cost.
Not Quite a Penpal
My camp penpal and I wrote back and forth for the better part of a year before it subtly tapered off, the way those things do. That's a different type of relationship than what Postcrossing actually offers, and the difference matters more than it first seems.
A penpal is ongoing. You build something — inside jokes, half-remembered context, a sense of who this person is becoming over time. Postcrossing, by contrast, is mostly built around single exchanges. You send one stranger a card; a different stranger sends you one back. Members can choose to keep writing to someone if a particular exchange clicks, but the system itself isn't designed for that — it's designed to keep introducing you to someone new. It's less "build a friendship" and more "collect a thousand small, brief ones," which is a genuinely different psychological experience than my penpal and I had.
I don't think one version is better than the other. But I do think it's worth naming that Postcrossing isn't really pen-palling with extra randomness — it's a different category of connection entirely, optimized for breadth and surprise rather than depth and continuity. Both satisfy something real. They're just not the same something.
How the System Actually Works
The mechanics of Postcrossing are worth addressing here, because they're part of what makes the psychology work. When you join Postcrossing, you're given the address of a random member somewhere in the world, along with a unique ID. You send that person a postcard with the ID written on it. Once they register it as received, you become eligible to receive a postcard yourself — from someone else entirely, at an unpredictable point afterward. It's not a one-to-one trade. It's closer to a chain, where sending moves you forward in line for your own surprise.
That design detail is worth sitting with. A direct swap — you send me one, I send you one — would remove almost all the unpredictability that makes this work psychologically. Instead, the system deliberately decouples sending from receiving, so the moment of "something arrived" is never tied to a specific person you're already thinking about. It's engineered uncertainty, on purpose, by a community that's spent two decades refining it.
It also addresses the obvious hesitation before it becomes a problem: yes, you're sharing your real address with a stranger. But it's shared with exactly one person at a time, never made public, and the system has run at scale since 2005 specifically because that controlled, limited exposure feels safe enough for people to actually do it. The structure is doing real psychological work — just enough vulnerability to make the connection feel genuine, just enough containment to keep it from feeling risky.
This isn't a fringe niche, either, even if it sounds like one the first time you hear about it. More than a dozen national postal services have issued postcard-themed stamps specifically tied to this community, and there's now an annual World Postcard Day with its own commemorative postcards and cancellation marks. A hobby built entirely around unpredictable mail from strangers has, over two decades, become something postal services design products around. That's a fairly strong signal that the psychology behind it isn't a fluke — it's something a lot of people, across a lot of countries, recognize in themselves.
If You Want to Write Postcards But Have No One to Send Them To
This is, I think, the real reason Postcrossing has grown the way it has. Plenty of people are drawn to the idea of writing — picking out a card, choosing words for someone — but don't actually have a long list of people expecting mail from them. A penpal requires finding a person first. Postcrossing removes that requirement. The system hands you a stranger and an address, and the only thing left to do is write.
That's worth noting if you've ever bought a beautiful postcard somewhere, fully intending to send it, and then watched it sit in a drawer for months because there was no clear "who." Postcrossing solves that specific, common problem directly — not by making you more disciplined, but by removing the part that was actually stalling you out.
I'm not a Postcrossing member myself, technically — I've never been assigned a stranger's address, never had that exact kind of surprise show up in my own mailbox. But I understand the appeal completely, and if you're someone who keeps meaning to send postcards and keeps running out of people to send them to, it might be the most direct fix available: free to join, no art skill required, no relationship to maintain. Send one. See how the waiting feels.
If you'd rather keep your postcard-writing closer to home — a friend who moved away, the person you've been meaning to write back to, or simply having something beautiful on hand for whenever the impulse strikes — that's its own version of the same instinct, just aimed at people you already know instead of strangers. Either way, the same small truth holds: you can't send a postcard you don't have sitting nearby when the urge actually hits.
Whether you're sending to a stranger through Postcrossing or to the people already in your life, having a steady supply of beautiful postcards on hand makes it easier to actually follow through. The Postcard Société was built around exactly that. Learn more here.
Dr. Katie Blake, PhD is a social and cultural psychologist, travel psychologist, and writer based in the US. She is the founder of The Postcard Société and the publisher of Psychologie, a publication on travel psychology, analogue life, and the art of moving through the world with intention. Available for media inquiries, expert commentary, podcast appearances, and brand collaborations — visit drkatieblake.com/press.