FWIW, I once got a letter sent to me from the US that had my name but no street address. They did, however, get my London Post Code correct and the postman delivered it without a hitch. He told me the post code got it routed to him for sorting and he recognized my name so he was able to know where it belonged.
The custom in most countries, especially in Europe, is to prefix the country code before the postal code, separated by a hyphen. For example, an letter to Switzerland would have, on the last line, CH-2846, or to Spain E-34080. But then, when writing from the USA, you have to put as the last line the name of the country in English, such as “Switzerland” or “Spain”.
Prepending the country code used to be the recommended method, but (at least here in Germany) it has been deprecated for some time. Nowadays you are supposed to put the name of the destination country, in capitals, on the last line.
There was an anecdotal story, some years back, that someone sent a letter to Herb Caen (late columnist at the San Francisco Chronicle), addressed only as:
(Icon of marijuana leaf) (Icon of man’s walking cane)
San Francisco
… and it got delivered!
ETA: IIRC, the originator of the letter was not in or near San Francisco. I don’t recall if it came from outside the United States.
Here’s even worse: Certain island places (Guam, Micronesia, Marshall Islands) have their own Social Security systems, and assign numbers that sometimes collide with American social security numbers. Creditors sometimes report deadbeats to the major credit reporting bureaus, using these numbers, which then ends up in the wrong person’s file, leading to major clusterfuck headaches.
Reportedly, Mad Magazine received a letter addressed only with a picture of Alfred Neuman on the envelope. I read this in their letter column years ago. Their response was “Take that, Playboy.”
Never heard of this, or practiced this, sending post to many countries.
In case it wasn’t already a call for captain obvious: The postmen read from bottom to top, that is why the last line is the destination country, then working upwards it gets more and more specific, until the first line is the actual person you’re writing. WWSHAT?
I can vouch for its existence. When I lived in Hungary, the recommendation at the time was to prefix the post code with “H” followed by a hyphen. That said, I don’t recall making the same sort of prefixes when writing to, say, Germany. ETA: Though, looking online, I do see some German addresses that do use the “DE-” prefix before the postal code.