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Blog > Postcrossing behind-the-scenes: address validation


As promised, the first post on our behind-the-scenes series is about address validation. This is the process through which we check that all addresses in Postcrossing are (to the best of our knowledge) correct and complete.

The Little Mail Carriers helping us moderate addresses

“Red alert! Red alert! I think that one over there is missing the postal code!”

Addresses are one of the most important things in Postcrossing. Wrong or incomplete addresses would result in postcards being delayed or not delivered, and general unhappiness – which we would like to avoid.

There is specialized software to process addresses of course, but it’s either dodgy, specific to a country or just crazy expensive for our size. So, we chose to do this task ourselves, splitting the job between Paulo, Vicki and I. Each one of us picked a set of countries according to our strengths and learnt the UPU address format of those countries by heart. Most countries have their own format – and some are much simpler than others. We use this knowledge to go over thousands of addresses per week, spotting invalid ones, or just rearranging the order of the elements on the address. Most of the time, addresses will be read by automated sorting machines, which expect them to be written in a certain way. So if every address is formatted as UPU recommends, everything will go faster!

What makes an address invalid? Lots of things:

  • Parts might be missing: name, postal code, country name, etc.
  • The address might be written exclusively in the local script (Chinese, Thai, Cyrillic), making it hard to write for people who don’t understand that alphabet or those without a printer.
  • The address might be completely translated into English – which is usually a bad idea. For non-Latin scripts, transliteration works better and faster in our experience.
  • The address might not match the account’s location/country.
Technology helps with the last item on that list, because we can usually match your IP address to the location you’re signing up from. For instance, if a member with an IP address in Canada is opening an account in Fiji … something might be wrong, and we have to look into that. :)

A few postal operators also provide a list of all valid postal codes for their country, giving us the ability to automatically detect typos or invalid postal codes.

The Little Mail Carriers helping us moderate addresses

“Let’s just add the country name here at the bottom… I think it’ll help!”

The whole process of validating addresses has been streamlined over the years, but it still takes quite a bit of time, since every single new address needs to be checked and validated. We’ve been doing it for so long that by now we can tell at a glance whether an address is valid, incomplete or just in a strange order. We might not find all the problems – but we do spot lots of them!

Plus, we’ve learnt many nice things in the process too! For instance, did you know that an address in China should be written from the biggest component (province) to the smallest one (adressee) if written in Chinese characters, but the other way around if written in Latin characters? Or that there are no street names in Japan? Or that every house and building has its unique postal code in Singapore? It’s amazing!

I think that’s it for addresses, so I’ll leave you with one last tip: make sure that you write the address on your postcard exactly as it is shown – it’s already optimized for that country!

I hope you liked this first post on our behind-the-scenes series – we’ll get cracking on the next one! :)

70 comments so far

FelipeDuarte, Brazil

What a huge work! Congratulations!
How come? No street names in Japan?

meiadeleite, Portugal

@FelipeDuarte: watch the video, it's really interesting to see the Japanese take on addresses: :)

Beautiful_Lie, Canada

Wow, awesome job guys! I really enjoyed this blog.

I work at a Security Department for Canada's biggest bank and I often have to send cards overseas... and we actually deal with courier services, so we can only work with civic addresses. I know how hard it is to memorize which countries have postal codes or not, what information goes where for Korean address and try to understand other languages to figure out the entire address (thank you Google!)

Keep up the good work, I know for a fact that it's not easy, but it's a fun challenge :)


danielc, United Kingdom

That sounds like a tortuous task, it's amazing the work that you do to keep Postcrossing running smoothly. I was recently told that Ireland is getting postcodes soon, most addressees there currently don't have any, each address will have its own unique postcode.

LuffieJJ, Netherlands

I always find it fascinating to see how addresses work. Of course addresses that are based on the Dutch system seem most logical for me. I'm always somewhat stunned with how long asian addresses can be, especially Indonesian!
The concept of no postal codes, street names etc is so weird to me

anitainge, Netherlands

what a grate job are you doing to make sure alle the members get there cards , thank you very much

LondonRain, Germany

I once read that the destination country should always be written in UPPER CASE. However not all addresses are formatted like that. Isn't that recommended?

CatharinaG3, Netherlands

Waw, that was very interesting! Nice to know more about those far-away addresses.
And what a huge work you have with the addresses already! When I think of the total number of members and new ones signing up... enormous. Could be a day job already.
Thank you so much for all your efforts!

And of course I'm looking forward to the next blog. :)

DorotheeB, Germany

Thanks for the information, so interesting to read. There is one thing that still confuses me: here in Germany we are told that the country should be written under the address. When I get an address from Russia there is always the postal code in the last line, the country is written above the postal code. So I wonder if the German mail system would realize this card to be send to Russia when the country is not in the last line?
And I am looking forward to the next issues of behind-the-scenes.

rosenbusch, Germany

Interesting informations....

meiadeleite, Portugal

@DorotheeB We once contacted Russian Post regarding the UPU official recommendation for Russian addresses, which features the postal code on the last line (below the country name). They explained to us that this is indeed the format they recommend, and that sorting is performed faster if the address is written like that.

Since in the case of Russia the bottleneck in the mail process seems to be the sorting done in Russia, it makes sense to optimize addresses for the destination.

manojkamat1857, India

I love German address ..

Portugal Brazilian Russian and Chinese addresses are fulll of Essay ..

Very thoughtful content .. always fascinating how such small team interprete false or faulty addresses
Thank u for Russian address trick ... Now my cards will move faster

aberline, Australia

Wow I had no idea! It's good to know they have all been validated!! So much work!

Lutje, Belgium

Wow, I had no idea how this worked!! Thanks a million times for doing this!!

devc, Portugal

Really interesting! I loved the video about Japanese addresses. Ty!

Sunneva12, Norway

thanks, this was interesting! also I love the small facts at the bottom :-)
looking forward to moore.


graugans, Germany

Fabulous! Very interesting facts. Love the video about Japan!

betslets, United States of America

Have you ever thought about writing a book (or an encyclopedia type work) regarding Postcrossing? Each blog would make a chapter (or maybe a book) in itself. The blog's attached video regarding Japanese addresses was reminded me of our own neighborhood subdivisions concept.
It's all makes for very interesting summer reading -- especially when it is so hot outdoors. Thanks.

azalee09, Germany

Thats really interesting. I print most of my adresses, just to make sure that the sorting maschines of the postal services can sort them right. I visited a distribution center of "Deutsche Post" a while ago and learnt that the automated maschines can identify only Latin letters.

SaskiaL, Germany

A huge work you do.... Fantastic
I always print the address and which provides little lost cards....

Elisabeth_, Austria

Wow, you validate every single address! So much work... thank you very much! I was also wondering about the Russian addresses - thank you for the info!

willyly, Hong Kong

I actually did sign up for postcrossing with my Canadian address when I was travelling in Hong Kong xD Very interesting article!

I'm actually very curious about Russian addresses too as their postal code is always written under the country name. I always wondered why...

AB-tje, Netherlands

Wat interessant om te lezen en te weten. Dank je wel voor dit tipje van de sluier.

Electric_Sheeps, Germany

Thank you for all the information. I feel now a bit smarter.
Foreign addresses seem sometimes so wrong and strange to me :D But since postcrossing I get used to it and also get a feeling for how they are right.
Haha... I also already drove my teacher with that a bit crazy as she wanted to tell me that addresses in every country have the same pattern :D I had plenty examples to tell her that she is wrong =)

Havarah, United States of America

Thank you for this post! It is really useful to read about all the work that goes into making sure that the addresses are accurate. There are sometimes when I have the temptation to put a part of an address on a separate line (because of space on the card) but now I know that maybe i should not! I will try to squeeze it in!

you all are fantastic.

KPost, United States of America

I liked this very much! I love behind-the-scenes posts!

frellathon, Australia

Thanks for all the work you do. I can't believe how much of it is hands on, the amount of time and effort put in is staggering. You guys rock.

Jarmo, Sweden

Very interesting and I'm looking forward to read more. Thank you for sharing this with us!

Maggie05, Australia

Thanks for the info, so interesting. I print my address but I still have cards that never get to the recipient --- there may be many reasons for that. Thank you to all the hard workers behind the scenes who make Postcrossing such an enjoyable hobby.

maroussia, China

As for Chinese addresses, the user should never translate it into English, but write it in "pinyin", that is the way it "sounds". The pinyin script is used for learning Chinese and for typing Chinese characters on computers (you type the pin yin and the code number of the character that is offered to you, and it prints a word in Chinese characters).

The addresses in English are more likely to be misinterpreted by the translators at the postal bureau. Very important in China is the post code. When you write to China from abroad, the most important is the name of the country. Please be careful to write either "China" or "People's Republic of China", as "Republic of China" means Taiwan and sometimes this creates problems (less now, when the relations with Taiwan are good and the mail goes freely).

As for the postal code, I cannot help finding strange to write it after the country's name, as it is something specific to each country, and for the mail employees in another country it means not much, while the name of the country you send the item to is essential......

Russian addresses are also written like the Chinese ones, from up to down, country, postal code, region if any, city, street, house number, flat number and then name. If you write it this way, I would advise you to add the country's name again under the name of the addressee. Same for Chinese addresses.

In some countries like Australia, if you write 1 like it is done in Europe, it is often confused with 7, while in Austria if you write it like in Australia (just a "stick"), the machine may not recognize it (I had a letter returned for that reason from both countries....).

In any case, it is best to write the name of the country you send an item to in the language of the place you send it FROM, or at least in English, or both. The local name of a country may not be understood by postal employees in another country. That means no disrespect for the language of the country. you send it to..... Then the rest of the address should be written in the language of the country you send the item TO!

CDNLib, Canada

Very interesting!! Thanks for enlightening us to all that you do and all that is required for all Postcrossing members to have such a great experience with this wonderful project. The video was very informative in a small amount of time - thanks!

ains, United States of America

So interesting! Thank you :D

Queenofeverything, United States of America

In the US, the bottom 1/2" of a letter/postcard needs to remain BLANK due to a computer-generated sorting barcode that is printed on the card during the sorting process. I have had several registration numbers written there that I've been unable to decipher which slows down the system for the sender and the recipient. Thanks for all the helpful info you provide everyone; I love Postcrossing!

whodalalee, Canada

Truly fascinating stuff! I wonder if I have messed up some addresses, because there was literally no place on my postcard to accommodate the 35 character address on one line... I usually write what doesn't fit on the next line, but indented...I am about to send a postcard off to Russia where the second line is 36 characters you think this is why some cards take so long to get there?
Thanks for the enormous amount of time you put into this project so we can all enjoy the treasures in our mailboxes!

troulala, Russia

To Maroussia:
You wrote "Russian addresses are also written like the Chinese ones, from up to down, country, postal code, region if any, city, street, house number, flat number and then name."

It is not so any more, since 2000 we write full name first, then name of the street, number of house, number of flat,
then name of the city/town/village, name of the district, name of the region, counry name (for international correspondance) and after that postal code.

But still even many Russians do not know about this novelty and write their addresses in an old way.

krishnaraosridhar, India

Very very cumbersome work... But, you're doing a great job... Hats off to your team...

lucymonty, United Kingdom

Very interesting, thanks for sharing! I want to work for Postcrossing checking addresses :-D

rosieam, Australia

Thank you.. this is so interesting :)

esmail, Egypt

thanks so much for this great project.

szancsi, Hungary

I am very pleased that this has been perfectly integrated system will improve on doing it! Thank you very much! I am glad that the world is here in my room through you!
Happy Postcrossing!

BxlPoster, United Arab Emirates

I have just moved to Dubai and I was slightly annoyed that Postcrossing blocked my account until I had entered an address compliant with local customs - but indeed only mail sporting a P.O. Box gets delivered here, as P.O. Boxes are the norm.

So I learned somethinf through Postcrossing I should have learned here from a post office - only there are no post offices here...


naobie, South Africa

Amazing...What an enormous job! Thank you so much. Very interesting read.

FairyFoot, United Kingdom

I've altered my address now, removing the county, and changed formatting.

hmthompson, United States of America

Why are British addresses so incredibly "layered"? Line after line after line . . .
then, up pops a simple 4-line address occasionally. Please explain.

cheshirekat, Canada

In Costa Rica many streets don't have names. only until recently they started to number the streets but not many people use them. So addresses are bit harder, something like "from the church in this city 50 mts north and 100 mts west" or "from McDonalds in this city, 300 mts nort right across from the pharmacy". we mainly use landmarks

siobhan, Germany

Very interesting read - I didn't realise validating addresses was such a big part of your job. Wow!

I wonder, as you say translation is not a good idea and addresses should be transliterated instead - why are there so many addresses especially from Belarus and Ukraine, but also from Russia, who have "xyz Street" and "Apt" in them instead of "ul./vul. xyz" and "kv."? And most postcards I sent to Moscow did have "Moscow" in the address, when I learned on the web site of the German post that city names should always be written in their original language, i.e. "Moskva". Or is it simply not a big enough deal for cities as well-known that they actually have an English name in the first place?

Sometimes I'm surprised by senders insisting on changing my address into a format that probably resembles what they know, like putting the postal code after the town (it's the other way around in Germany), or on a separate line even. Sometimes I suppose that's because the address field on the card has a box for the postal code and people write it in there out of habit, even though it's in the wrong place for the address at hand. The good news, however, is that I can only marvel at it because those postcards got to me anyway. :)

FairyFoot, United Kingdom

Cheshirekat's comments reminds me of a Terry Pratchett Discworld novel, Going Postal.

Red_and_Green, Poland

It is astonishing how much work you do! And it leaves me speechless that you have managed to validate all of these 488 000 of our addresses, and learnt the address formats of so many countries by heart! That is truly impressive... RESPECT! And a big thank you.

I find addresses fascinating, so I read your post (and the comments) absorbedly. I enjoy writing addresses myself :) The more weird an address, the better ;) However, sometimes I have doubts if they are correct... Now I know they are :) But when an address is long and complicated, sometimes I need to send a different postcard than I originally intended to, as there is not enough space for the address on it...

A couple of times I received a postcard with lines in my address separated in a quite unusual way... Fortunately, it didn't stop the postal service from delivering them safely to my mailbox :)

Someone mentioned the differences in writing 1 and 7. In my address there are a few 7's and when I receive a postcard from Asia or the USA, to me they look like 1's =) I always feel lucky that the postcard didn't end up in my neighbour's mailbox or in another city ;) When I send my postcards to these parts of the word I always try to remember about writing these numbers distinctly.
Once my friend, who has "43/1" in her address, got a postcard where "/1" were two vertical lines, which looked like "4311" or just "43-and-two-lines" ;D Luckily, her postman was a smart guy =)

PS. I love addresses in Costa Rica, they are almost poetic! :)

Amiya, India

Wow, what a mammoth task! And it has to be just perfect, else some eagerly sent postcards may be lost forever in the dusty lanes of a wrong address. Thank you for what you do. :)

manbol, India

Thanks...It was interesting to read about the Address. It's really a great deal of work you do behind the screen.

wildernesscat, Israel

What is the situation with Crimea, postcard-wise? Are they still addressed as "Ukraine", or did they become "Russia"?

YiliLoh, Malaysia

Thanx for the interesting info. :)

Luziaceleste, Brazil

It makes a lot ofsense to optimize adresses! Great job!

RosaRosae, Spain

Mail that has no clear addresses and can not be sent back to the sender stay for a time in post offices files ( in case anyone claim it ) after that time they are destroyed.

RosaRosae, Spain

Sorry I say wrongly "anyone" instead of "Receiver"

meiadeleite, Portugal

@wildernesscat They're still using the UA country code (as the ISO 3166 norm which regulates these things hasn't been updated yet).
In practice though, things have changed and only mail addressed to "Crimea, Russia" seems to arrive. We've explained the situation here:

Franciscaatje, Netherlands

Great read! Thank you. In the Netherlands we really have a great postal code sytem. The most important part is the postal code. If you would only put the country, the postal code plus housenumber the card will arrive! We also have the system as mentioned by Queen of everything/USA: a computer-generated sorting barcode that is printed on the bottom tight half of the card during the sorting process. So if an ID is put there , you often cannot decipher it.

Avrilnolte, South Africa

Very interesting article about the postal codes and thank you for your hard work!

Is there a place on the home page where all the greetings are listed? I like to greet people in their own language - and mine!

Red_and_Green, Poland

@Highbird I may be wrong but as far as I know "Suomi" is the name of this country in Finnish, while in English it's "Finland". Since the English language is now used worldwide, in international shipment we use its English name. Just like we write "Germany" rather than "Deutschland", "Hungary" instead of "Magyarország" or "Japan", not "Nippon" or "日本". The name must be understandable for postal service workers all around the world, not only in the country of destination.

Here in Poland our postal service recommends writing countries' names both in English and in Polish. When I write an adress in the Cyrillic alphabet I write the name of the country even three times - in English, Polish and in Cyrillic =)

danielc, United Kingdom

@dove It is more correct (according to Royal Mail) to use the post town and postcode and omit the county. Postal counties were abolished in 1996 and often didn't correspond to actual counties anyway.

Where I live in north London, the postal county was Hertfordshire, even though it was transferred from Hertfordshire to Greater London in 1965. However, it isn't correct for me to put 'Greater London' as part of my address, as I don't have a London postcode, I am in the Enfield postcode area (EN) and my post town in Barnet.

Similarly, many people in parts of north and west London had Middlesex as there postal county, even though this county disappeared from the map in 1965, they should more correctly just use there postal town (e.g. Enfield, Hounslow) and postcode.

Amiya, India

Loved the YouTube video on Japanese addresses (and other opposites) that Ana shared!

fionat, United States of America

My local post office says that the machines in us post offices will mistake postal codes from other countries for the us zip code, so always put the country name below it. But maybe I will make an exception for Russia. Thanks for all your hard work, and for sharing it with us!

kindheart, United States of America

Very interesting, we learned something new today! Thank you!

hankadl, Czech Republic

Wow! I wondered if the process was authomatized... I admire you guys for what you do for postcrossing.

FillyCat, Indonesia

@LuffieJJ Yes, we do have a long address. I, myself, wished that address in Indonesia could be simpler. But that long address just to make sure that the mail arrived safely to the correct person :) Although I do have a few mails that still lost somewhere. The problem is, sometimes, a lot of people don't know their own post codes or their complete address detailing in Rukun Tetangga (abbreviated RT, which is similar to neighborhood, consists of 30 to 50 households), Rukun Warga (abbreviated RW, which is similar to neighborhoods, consists of 8 to 16 RT), kelurahan (which is similar to village, consists of at least 900 households), kecamatan (which is similar to district, and where postcodes are divided by it), city, and country. So, now you see why we have a long address :)

To Postcrossing team : Kudos to you..! :) I can just imagine what kind of headache it could caused you to sort all those addresses. Thank you so much for all the hard work :D

nugget, United States of America

Wow! I never knew it was so much work. Thanks for checking the addresses to make it a better experience for all of us.

eleanor16, United States of America

Thanks for all you do! Who knew how complicated an address could be. Thanks again for 6 years of happiness!!!

martinberlin, Germany

Very interesting article - thank you. I am missing one information: when does this validation takes place? Everytime when a new postcrosser joined or someone changed the address? Immediately after a few days?
Or only when there seems to be any problem?

And I would like to know something about how you decided to handle with addresses from the Crimea?
Today I've got an adress with the country "Ukraine", but the address was an address with a Russian ZIP-code and with "Russian Federation" as country instead of "Ukraine" or at least "Autonomous Republic of Crimea"?

paulo, Portugal

@martinberlin: Addresses are validated in both cases: new address (sign up) and when an existing address is updated since both require validation. We do not wait for problems to occur first, so addresses are always validated beforehand.

Regarding the Crimea (peninsula), Ana has explained the situation here:

In Postcrossing we use a ISO standard to, among other things, determine the 2-letter country codes used in Postcard IDs and Crimea is within the "UA" code:

However, in practice, international mail can only reach Crimea if routed through Russia (using a Russian Post 6 digit postal code) since the Ukraine Post is no longer able to deliver mail to that area. So, for this exceptional situation, we accept addresses in Crimea with "Russia" even if the account is under the "UA" country code. This way postcrossers in Crimea can continue receiving mail.

fdrake, United States of America

This is a great discussion; thank you!

For the more geeky among us, it would be interesting to learn what you found regarding address verification services around the world. I know good services tend to be difficult to find, and are often targeted for mass-mailing operations.


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