Definition
A dead letter is a piece of mail that cannot be delivered to the intended recipient. This happens when the address is incomplete, illegible, or outdated. âī¸ Think of it as mail that's lost its way home. These letters end up in a 'dead letter office' where postal workers try to find a way to deliver them. If all attempts fail, the letter is usually destroyed or, sometimes, opened to find clues. It is the postal equivalent of a lost soul.