I used to use a website where you could send a postcard to a randomly assigned address of another site member on there, and in return you’d get a postcard back from a different random member. One time I wrote the address too close to the stamp area so I could only fit one stamp up there, and had to put the remaining stamp postage at the bottom, and then I dropped it in a mailbox in town somewhere.

Japan Post missed the extra stamps at the bottom and so returned it to my house, despite it being a postcard with no return address to a random country I had no connection to. I lived in the boonies so there weren’t a lot of foreigners in town, but there were definitely at least a few others.