A bounce message or just "bounce" is an automated message from a mail system, informing the sender that the sent email had not been delivered (or some other delivery problem occurred). The original message is said to have "bounced".
Errors may occur at multiple places in mail delivery. A sender may sometimes receive a bounce message from their own mail server, reporting that it has been unable to deliver a message, or alternatively from a recipient's mail server reporting that although it had accepted the message, it now finds it undeliverable - when a server accepts a message for delivery, it is also accepting the responsibility to deliver a Delivery Status Notification in the event the delivery fails. For various reasons, particularly forged spam and email viruses, users may receive erroneous bounce messages sent in response to messages they never actually sent. Source: Wikipedia
Bounce messages often have the following (or similar) descriptions in their subject lines:
- Deliver Status Notification (Failed)
- Delivery Notification: Delivery has failed
- Delivery Status Notification (Delay)
- failure notice
The content of a bounce message will usually describe the reason that the email could not be delivered. The original email or sometimes just the headers of the original email are usually included with the bounce message, sometimes as an attachment.