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Blog > Postcrossing behind-the-scenes: unknown Postcard IDs


On the last behind-the scenes post, many of you asked how do we find missing Postcard IDs. Well… I’m afraid the answer is pretty straightforward: for every help request you submit, we compare the information you provide us about the postcard you’ve just received with all the information we have about the postcards currently traveling to you until we find a match.

There aren’t any magic tricks for this one – it’s just a matter of patience and sharp Sherlock-skills!

Let’s see how it works in practice. Imagine it’s 2005 and someone named “Ana” has just received a cute postcard from Portugal with some lighthouses… but sadly, the Postcard ID is wrong, and she cannot register it. She knows what to do though, and promptly submits a request for help with her unknown Postcard ID!

On Postcrossing’s back office, a page is created for her help request. It looks a bit like this:

Finding missing Postcard IDs

This page is only seen by us, the members of the Postcrossing team, and contains all the information we might need to find the right postcard ID.

On the top of the page, you see all the information Ana just submitted about the postcard: it features 3 lighthouses, was sent around July 6th, from someone named “Paolo” from Braga, Portugal, who mentions he’s an IT student.

Then, below that, a neat little table is displayed with all the postcards traveling to Ana. For instance, you can see she has quite a few postcards traveling to her at the moment: a few from Portugal (shown first, since they are most likely to match), one from Germany and one from the Netherlands.

Can you guess the right postcard ID for the card Ana received? Given all this data… it’s not that complicated, right? You just need to compare the information available to spot the correct postcard ID!

So it looks like PT-1 is the postcard ID she was looking for: the ID is very close to the right one, the name and location match, the picture the sender uploaded seems to fit… now all is left is to let the recipient know this information, which we do by clicking a button.

If enough information is provided, Postcrossing can sometimes automatically find the right postcard ID, but most of the time, things aren’t so simple — that’s where Vicki steps in. She goes over nearly 1000 requests every week, going after the really tricky cases and doing some remarkable detective work to make sure all postcards are registered. It’s a very time-consuming process, but a very important one as well, which minimizes frustration all-around.

So… what are the most common problems she has to deal with?

Most of the time, simple stuff: digits are out of order, a 7 looks like a 1, a number might be missing, someone wrote the ID of the next card they requested or there might be some confusion regarding country codes (CN≈CH, AU≈AT). Sometimes, in the excitement of sending off a postcard, someone will just forget to write down the postcard ID. Given enough information, the answer is usually straightforward.

But there are trickier cases — like when you receive a card from a private swap which you completely forgot about! Or when members don’t realize that the postcard they received was actually sent to a roommate or family member living in the same address… in which case, every family member should submit a request.

A few postcards do arrive after traveling for over 1 year… in which case they cannot be registered.

What helps? Here are some tips on how you can help make a search for a Postcard ID more efficient:

  • Describe the image on the front of the postcard you’ve received in as much detail as possible! If your description matches an image the sender has pre-uploaded, the search for the right Postcard ID will definitely be easier.
  • Can’t make out the exact name of the sender? Have a guess from the signature. Even if you write it incorrectly, we’ll probably be able to figure it out.
  • Look closely to the stamp and cancellation mark. Where and when was this card posted?
  • Does the postcard describe the sender, eg. what they do for a living, where they live, whether this is the first postcard they send? If so, include these on your help request!
  • Submit just one request per postcard received. If you want to add more information to it, just delete the request (you can do this on your Received postcards page) and re-submit it with all the information.

To prevent this situation, here are some tips of things you should do, which will definitely help your cards get registered in case something goes wrong:

  • Try to write the Postcard ID with a pen with water-resistant ink, so that it cannot be washed away if the card gets wet.
  • Write the Postcard ID on the left side of the card, and at least in two different places.
  • If this is a card for a private swap, or a thank you card – mention this on the postcard, so that the recipient does not confuse it with a Postcrossing card!

Every time a help request is submitted, the status of the search will show on your Received Postcards page. If it says “Searching”, then it is still in the queue and will be answered as soon as possible. If you manage to find out the right postcard ID before we gave it to you – congratulations, you must be a smart cookie! :) Just don’t forget to delete your request for help on the Received Postcards page.

Finally, it seems many people are still unaware that they can ask for help searching a Postcard ID… so if you see any pleas for help on members’ profiles, just pass on the knowledge and share the link to our special form, deal?

56 comments so far

radiofan, Austria

Good to know that discribing the picture is useful information! -
Thank you for all your great support and your awesome project! Postcrossing is wonderful!

kugusch, Germany

another awesome article!
In past help requests I'd only mentioned the image of the card if it was a view card that might pinpoint a location of the sender...I never thought about you being able to see uploads and being able to match cards simply through I learned something new for future requests.
One suggestion for improvement (if it hasn't been done already): In the past I've had cases where I could only make out partial send date information, but the system wouldn't let me enter just a month/year or just a day, it was all or nothing.
Thanks for the great article!

taxcha, Indonesia

This is very nice to know, thank you Postcrossing Team for all the hardwork!

dollart, Finland

With help of postcrossing staff several unclear cases has been solved for missing id¨s or some diggets wrong with id. thank you very much. Keep up the good detective work.

Sunneva12, Norway

Lovly post, I love reading. I sometimes just write the ID one spot at the postcard, so I'll start getting better to write it on 2 places! anyways the post is interesting, didnt knew you coud have a look on which postcard were traveling to who!

happy postcrossing!

kroete68, Germany

Thanks to Vicky and the team for doing this detective work for us. And good to know, that the picture also can help finding the ID.

And of course: deal! :)

pucky, Netherlands

I have been helped already a few times in very little time, thanks a lot! Great service!!

LindavG, Netherlands

Great behind-the-scenes post! I myself am very curious about the algorithm behind selecting the postcards!

scrutiny, Hong Kong

You guys on the postcrossing team are awesome. :)

EggsTheBest, Canada

Somehow I never thought about describing the front side of the card, only the back. :)

I wonder, why is it impossible to register a card that arrives after over a year?

RominaGundersen, Portugal

Nice to see PT-1 card! :)

anagahan, North Macedonia

this feature has saved me both ways on a number of occasions...funny, I've never thought of entering information about what the sender wrote, like what s/he does for a living, how old they are etc...I usually just tried to figure out the name, but this extra option would be taken into account in the future...thanks a bunch!!

kelpie, Russia

Thank you for the article!

What do you think is it a good idea to write the sender what was wrong with the ID? It looks like postcrossers never do that. But I'm always curious after receiving a letter from support about wrong/missing ID on my card.

Nettydel, United States of America

I've been helped with this twice already... once some one sent me one without ID, and once I mixed the numbers on one I had sent out. Awesome work you all do to sort them all out. I LOVE Postcrossings!

Queenofeverything, United States of America

I love learning about the background of what goes on in daily Postcrossingland! Keep up the good work and information--in the end, it benefits all of us 8-)

HofVliet, Netherlands

I have used this service a number of times, and it works great.

The first mistake I made when I was still using to accounts, I tried to register my very first card on the wrong account.......

lyndac, Canada

I think an important prevention is writing that it is a swap or a thank you on the card. I reported one once and it was someone sending me a card because they liked the one I had sent and I had put my return address on it because I had a few expired cards.

rosenbusch, Germany

Thank you for the interesting informations....

SoupLike, Lithuania

Thank you for this post! It might seem pretty straightforward to you, but it actually was a bit of a mystery to me (imagining the search was somehow less manual). On the other hand, I will be more appreciative from now on if/when I require this particular service again. Hell, I would actually enjoy such a detective work myself! :)

By the way, LindavG mentioned that she'd be interested in Postcrossing's postcard selection algorithm. I'd be glad to learn a little bit about it, too! ;)

tsvetana, Bulgaria

I thought there's some kind of a database (e.g. Oracle database) where the "match" between username of sender, username of recipient and ID of the sent postcard are logged. It would be much easier and faster not only to track postcards with wrong ID, but would enable you to make more types of statistics. Of course, the current way is much more fun, but just saying... :)

ChalkJunkie, Germany

Thanks for letting us in on your secrets :-) I really enjoyed reading this article and I always appreciate your prompt help when I can't register a card. And of course a special thanks to Vicki for being Postcrossing's personal PI.

Shazza1532, United States of America

Thank you for helping me get postcards and send postcards with the right id's!

paulo, Portugal

@tsvetana: That is already done - all traveling postcards are tracked (as shown on the mockup), but that is not enough to know which one you just received without a Postcard ID in it from all the ones traveling to you.

Keep in mind that at any given time there might be multiple postcards traveling to the same person coming from the same country - and it can even come from people with the same first name as some names are more common than others.

There is some automation already in place to make guesses based on the information that was submitted, but it can easily hit multiple matches, incoherent information or simply not have enough enough information to make a clear (automated) choice. When that happens, it the process has to be done manually as to not incorrectly "guess" the wrong Postcard ID and send it to the person who requested help which would then register the Postcard ID for a different postcard that probably didn't arrive yet.

HM, Netherlands

When I come along 'received a card with a missing or incorrect ID' written in the userprofile, I use to sent a message to the user to attent them on the Postcrossing Search the ID- service.

I have used this service several times, as sometimes cards are delivered with damages or because of not waterproof ink.

Or whatsoever. Not to mention bad-handwriting~~~ (mine as well). And some countries have very loooong ID's, therefore I prefer to receive cards with short ID's!

Sometimes there are 10 cards from the same country travelling to me, it must be a challenge to find the correct ID then - the ID's are sometimes very simular!

Good work and compliments for the team!

Luziaceleste, Brazil

This help really works, and I never figured out that uploading the postal image I would help somehow...Very interesting information, thanks for the care!

Divergent, Türkiye

Awesome article !

OnTheMoon, Italy

Thank you very much for this post and for the advice! It actually never came to my mind that describing what is shown on the picture or details about the sender could be helpful in identifying the ID!
And of course, thanks for all your efforts, Sherlock Holmes would be proud of you!

fisherman, Ireland

I use the service quite often and many thanks to Vicki for the trojan work she does on the difficult cases.

uglyspinster, Germany

Very interesting! And thanks a lot for all your good work! A while ago I received a card from Belarus with clear ID which I was unable to register. By checking IDs nearby I found out that the card was travelling for over a year.
I submitted a request anyway asking if Postcrossing could tell me the sender's username so I could thank them and it worked.
Of course I was a bit sad that I couldn't register the card but at least I could send a thank you message.

Red_and_Green, Poland

Thank you for another interesting article which unveils the secrets of your fascinating (and hard!) work and gives us an insight into the "machinery" that allows us to do what we love - sending postcards! :) And a big thank-you to Vicki who has already helped me twice with ID numbers and with other problems as well :-) Now I know what information to include to make her work a bit easier.
And I'm curious about the postcard selection algorithm too =)

JoKo61, Australia

The very first card I sent I didn't put the ID on, I thought the ID was just for me to keep track of the cards. Now I know. I also know that every request I've put in to find a sender is replied to almost immediately. It also taught me to put the number at the top left corner, and the other place I put it is writen horizontally between the address and text. I LOVE POSTCROSSING.

Paperinik, Italy

I do this when I receive a postcard sent more than one year before:

ZenCat, United States of America

This is a very useful feature, and the Postcrossing team successfully found another ID for me today :) It's nice to see what goes into the search!

Irip, Russia

good job, Sherlock!)
i love you guys, postcrossing is great!!! keep on!

YiliLoh, Malaysia

Wow! The team has done a good job forthe postcrossers! Salute!

jjajja88, Malaysia

I had requested 2 times. :)
The first card, the id missing 1 number, I requested the right id and got it in a short time :) The second card was my own mistake.. hehe.. I requested for the right id and the result was, the admin can't search for it. After a while, i noticed my mistake, I registered the card and cancelled my request.
The steps to request the missing id is easy if the sender give enough information but it might turn otherwise.

topcloud, Kenya

Great story! I love you, Postcrossing team. Asante sana!

Stasele, Netherlands

A great blog entry. I've always wanted to know how you do it. You've helped me a lot with some of my postcards. And I have made some mistakes with addressing mine (shame) - so you probably helped my addressees too!

You might want to post an entry on how it all began. Do you remember the first card with a missing /incorrect ID you tracked? Was it easier or more difficult in the beginning?

Keep on the great work!

knally13, United States of America

Great post! I'd also love to know more about the address selecting algorithm :)

ned44440, Ireland

Great to hear how this fantastic service is operated. Vicki must get great job satisfaction from her day. Like quite a few Postcrossers here I never realised that describing the picture on the card might be of any use at all.
Just yesterday I had to log two postcards when I couldn't register them because of incorret IDs. Both were traced before the ink was dry on my email. I have been known to write the incorrect ID myself on ocassion. My usual trick is to reverse two digits.
I usually write the ID on the card three times in a different colour biro than the one I used to write the text. Often I will have my first name on the card twice - once in the body of the text and once as a signature. I also include my user name as well and my location.
I am enjoying this series of blogs. Keep up the excellent work.

Red_and_Green, Poland

I've just found out that this is the actual very first Postcrossing postcard! Wow! Awesome to see it... It's a part of history now...

Just like ned44440 I always write my name twice, put the name of my city and the date... Never write the ID number near the address area to avoid any confusion with the postcode... I try to write the ID in two places but sometimes I lack enough space for it... I am a talkative person, can't help it... ;P =D

Roadrunner73, Germany

Thank you very much for the information. You are doing a great job (I also had a few cards where I needed your help).

krishnaraosridhar, India

A very great job by the PC team which is going on behind the scene... Royal salute to the team...

Luciano, Brazil

Thank you for informations! Very good.

ElinaA, Finland

I always write the ID in the middle of the card, vertical. Hope this way it does not get lost even if the card gets damaged and part of it rips away. And vertically so it doesn't get confusion with address. :)

isagv, Germany

Love "behind-the-scenes. :)

RandomDriver, United States of America

Sooo...the take away is...upload pics of your cards before you put them in the post, Mention your town, and Country..Seems simple....and yet I am guilty of missing this stuff as well. :(

Tetsuko, Germany

This article is great. Love it. And I meet so many people not knowing about that service so I hope this article will make it a bit more known among potcrossers.

I look forward to the next "behind-the-scenes" article.

moonlessnite, Canada

A very appreciated endeavour...and Vicki, I hope you don't resign from this task...thanks for all the times you have helped me register some awesome cards.

froukjeb, Germany

Thank you again very much for this behind-the-scenes article. As another member said as well, this job sounds like great fun to me! If Vicky ever needs help, because there are too many requests, I´ll be happy to offer a helping hand :-)

juttertje, Netherlands

I've just received a card without an id and after reading this topic I added a description of the card.
Thank you for sorting this out.

killewips, Germany

Thank you for this really interesting article. It's good to know that it helps if the sender uploads the picture.

betslets, United States of America

As usual, Postcrossing provides something I'm sure many of us take for all do a tremendous amount of work to help make things FUN for everyone. What I'd like to see in an upcoming blog/behind the scenes is "The history of Paolo and Ana". (Perhaps this has already been incorporated into a book? Could it be titled "PT-1"?
BTW, I'm among those that has required assistance in finding missing/unknown IDs and you are all appreciated.

jean-jacques, France

Thank you for your work.
I already used this service

wulandani, Indonesia

great information, i have already used this service and succeded.

nugget, United States of America

Thanks for the informative article. I enjoy learning about what goes on behind the scenes. And a big thank you for this service. I have benefited as a sender and as a recipient.


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