Bounce message
（重定向自Delivery Status Notification）
![MTAs involved in a reject are named according to the point of view of the Reporting MTA. MTA names are often of type dns.](/Images/godic/202501/08/Bounce-DSN-MTA-names1544.png")
In the Internet's standard email protocol SMTP, a bounce message, also called a Non-Delivery Report/Receipt (NDR), a (failed) Delivery Status Notification (DSN) message, a Non-Delivery Notification (NDN) or simply a bounce, is an automated electronic mail message from a mail system informing the sender of another message about a delivery problem. The original message is said to have bounced.