undeliverable

Undeliverable describes items, messages, or communications that cannot be delivered to the intended recipient after standard delivery attempts. The term applies across contexts such as postal mail, electronic mail, and parcel shipments, and it is used in both logistical and messaging systems to classify failures in delivery.

In postal services, undeliverable mail can result from an invalid or missing address, the recipient having moved, refusal of delivery, or the item being deemed undeliverable for other reasons. After delivery attempts fail, shipments are often returned to the sender, placed in a holding facility, or sent to a dead-letter office where further action may be taken.

In electronic mail, undeliverable messages are indicated by bounce notifications or non-delivery reports. Causes include invalid addresses, non-existent domains, full mailboxes, or server-side filters that block delivery. Bounces are categorized as hard (permanent) or soft (temporary). Senders can correct the address, obtain consent, or adjust mailing practices to reduce future undeliverables.

For parcel and courier services, a delivery attempt can be unsuccessful due to an absent recipient, access limitations, or improper labeling. Carriers may attempt redelivery, hold the package for pickup, or return it to the sender, sometimes after several attempts or additional fees.

Impact and management: Undeliverable items affect service metrics, inventory, and communications planning. Organizations track undeliverable rates to monitor address quality and to comply with regulations governing returns and consumer contact preferences.