Most undelivered mail goes to the Mail Recovery Center of the U.S. Postal Service in Atlanta, Georgia. The center is the official lost and found department of the postal service and used to be called the "Dead Letter Office."
Examples of undelivered items that are sent to the MRC include loose items valued at $25 or more, cellphones, guns, eyeglasses and new or expensive clothing. Government-issued documents, such as birth, death and marriage certificates, that are found loose in the mail also go to the MRC. When it is possible to locate the sender of important documents, such as blank checks or bank deposits, those documents are returned to the sender or to the bank.