From Australia, there are 5 (main) postal routes into the USA. East Coast, Westcoast, Western Canada, East Canada, and Mexico.
Spelling out the state name helps international mail-sorting to get US-bound mail into the right centers. Most non-USA people don’t know USA state names and abbreviations.
Spelling out your state name helps senders and the international postal system get your postcards to USA recipients.
Hopefully the senders would be writing a “USA” on the bottom line of the address to make it clear? 
USA gets letters to the USA, but it could be the wrong distribution centre
I don’t think mail from Oz to USA goes via Canada or Mexico?
What about from every other country?
State Abbreviations are more likely to go to the wrong dist-centre than state names.
USA doesn’t get mail to the correct disctribution centre
It’s my understanding that the zip code is far more important than how the state is written. Once zip codes began being used in the 1960s the USPS switched to using the abbreviations for states. I don’t think writing out the state name will help with faster delivery.
You can read more here:
Seems like Australia needs to streamline its system.
What about Europe, Asia, Africa?
Post codes become relevamt once the mail arrives in USA.
International post coming into USA, needs state name and USA
I guess it’s possible. Mail service really sucks these days, so I wouldn’t doubt we’re having it processed in Mexico or Canada before it reaches the USA.
Yes.
Hmmm…I don’t see how spelling the whole state gives postal services more info than abbreviations unique to each state. Do you think all postal workers know where all the US states are if they read the name in full (especially vs if they have a chart with 2 letter abbreviations?) and they decide what distribution center to send it to based on that? That doesn’t make sense to me. Does any postal system anywhere say that spelling out a US state name in full speeds up delivery or is this an idea you had on your own? Granted, I don’t work for any postal system. Maybe one of the several postal workers/mail carriers who are active on this forum could shed more light on the subject.
I do know that for my address the city + full state name + zip code would be too long to fit on a line on a postcard. True, the zip code could drop down to its own line but then my address goes from 4 manageable lines to 5 for people to fit on a little postcard.
The recommendation issued by the UPU is to use abbreviation. And I think for postcards they’d just follow wherever the higher priority shipments go, wherever it is. So other than the name of the country there isn’t much to help. I don’t think the delivery would go any faster.
But this is just a personal impression, I don’t know how international post works and how they chooses a route each time they deliver something.
I’n not sure this is totally accurate advice. The average Australian citizen might not know their MA from their MO or whatever but the mail sorting systems do.
I would assume that if Australian postal sorting machines are programmed to direct U.S. bound mail into the right centers, based upon the full name of the state, then I would think that it would be quite easy to also program those machines with each state’s abbreviation. (By the way, all U.S. bound mail sent from overseas arrives at one of five International mail processing facilities in the U.S.; in L.A., (or Los Angeles, for those who prefer the full name), Miami, Chicago, San Francisco, and New York).
That recommendation to the UPU is from the USPS.
Postcrossing moderates the addresses as per the UPU recommendations, so we only accept 2 letter abbreviations for the USA States.
By formatting and using the address as advised by a specific country’s postal service the sorting process is quicker as the sorting machines are set up to recognise a specific pattern.
Postcrossing will only accept US addresses with a 2 letter abbreviation for the State name as per the UPU and USPS instructions.
Vicki
Postcrossing Team
Incorrect.
International mail coming into the USA (or any other country) needs the country written clearly and for the USA the USPS actually says the country name is United States of America.
Mail to other countries is sorted by country into huge mail crates/sacks and then when the container is full the mail is dispatched to that country along a route that the mail authorities have set up between them selves. It is only once the container has arrived at the relevant country that the sack is unpacked and then sorted internally to the final destination for delivery.
The sending country does not sort a different countries mail into their distribution centres.
Vicki
Postcrossing Team
I infer that this thread was created as USA has multiple postal entry points, with the idea that writing out the state name somehow prevents the card from being sent to the other end of the country. I don’t believe it works that way, rather the first digit of the postcode would be used for any pre-sorting. Even if it did go through the ‘wrong’ entry point, that would make a difference of a couple of days or so … usually.
As for name of country, almost everyone uses USA (plus local equivalent sometimes), with United States of America rarely seen.
so true. Even within the USA. I sent out a Christmas card last November and got it back as undeliverable this June.