Bounce Mail:-

              Bounced mail is an e-mail message that has failed to reach its destination and therefore such e-mail messages are returned to the sender. The message “bunces” back to its sender from the mail server after the server fails to located the message recipient address.

             The bounced message alerts you that your e-mail has gone undelivered and that you must again send the message with the correct address in order to ensure that your message reaches its recipient.