I think it's just one of those factoids that gets passed around through pop-culture because nobody takes the time to verify it.
Before reading the Snopes page just now, I would probably have said that I was pretty sure mailing cash was technically illegal. But thinking about it now, I have no idea where I got that idea from.
The Postal Service advises against it. You probably heard some postal official say "Don't mail cash" and mistook it as a citation of law rather than simple advice.
Before reading the Snopes page just now, I would probably have said that I was pretty sure mailing cash was technically illegal. But thinking about it now, I have no idea where I got that idea from.