Undeliverable Mail refers to mail items that cannot be delivered to the intended recipient for various reasons. Common causes include incorrect addresses, the recipient moving without leaving a forwarding address, or the recipient refusing the delivery. When mail is undeliverable, postal services typically return it to the sender or hold it for a certain period. To manage undeliverable mail, postal services often use a system to notify senders about the issue. This may involve marking the mail with a label indicating the problem, such as "Return to Sender" or "Address Unknown." Proper addressing and timely updates can help reduce the occurrence of undeliverable mail.