Bounce message
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A bounce message, or Delivery Status Notification (DSN) message, is an electronic mail message sent by the mail system itself, to indicate that a message could not be delivered. The original message is said to have bounced.
One reason that mail can bounce is if the recipient address is misspelled, or simply does not exist on the receiving system. This is a user unknown condition. Other reasons include resource exhaustion — such as a full disk — or the rejection of the message due to spam filters.
Bounce messages in SMTP are sent with the envelope sender address <>, known as the null sender address. They are frequently sent with a From: header address of MAILER-DAEMON at the recipient site.
Typically, a bounce message will contain several pieces of information to help the original sender in understanding the reason his message was not delivered:
- The date and time the message was bounced,
- The identity of the mail server that bounced it,
- The reason that it was bounced (e.g. user unknown),
- The headers of the bounced message, and
- Some or all of the content of the bounced message.
Related RFCs
RFC 1894 (http://www.ietf.org/rfc/rfc1894.txt) - An Extensible Message Format for Delivery Status Notifications
RFC 3461 (http://www.ietf.org/rfc/rfc3461.txt) - Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs)