Deadletter

Deadletter refers to mail or messages that cannot be delivered to their intended recipient and cannot be returned to the sender or forwarded. In postal service practice, such items are set aside for a special handling process and are not treated as regular outgoing mail.

In many postal systems, a dedicated unit known as a dead-letter office or dead-letter branch handles undeliverable items. Clerks review the exterior address and, when allowed by policy, inspect the contents to identify a forwarding address, locate the sender, or obtain information that might enable delivery. Privacy protections and legal requirements guide what information may be opened or examined. If no resolvable address or identification is found, the item is disposed of according to regulations, and some contents may be preserved, sold, or donated in appropriate cases.

In computing and information technology, the term dead-letter is also used in reference to a dead-letter queue (DLQ). This is a holding area for messages that cannot be delivered to their destination or processed by downstream systems. Reasons include invalid addresses, expired tokens, failed authorizations, or content errors. The DLQ enables operators to analyze failed messages, diagnose problems, retry delivery, reroute to alternate destinations, or discard the items without loss of system integrity.

Overall, deadletter describes items that cannot be completed through normal delivery paths, whether in traditional mail or modern messaging systems, and represents a controlled mechanism for handling such failures.