Elvis Presley's 1962 hit "Return to Sender" from the movie Girls! Girls! Girls! holds true today. If you get unwanted mail, simply write "Return to Sender" on the unopened envelope or parcel and the Post Office will take it away, no additional postage necessary.
I've had mail returned with the "Return to Sender" stamp when I've used an out-of-date or mislabeled an address. Takes a while, but it does come back.
ABCs of Letter Writing / R = Return to Sender
Today is National High-5 Day - Give a high-5!