Bounce message
The email a sender receives when a message could not be delivered, typically from MAILER-DAEMON or postmaster, naming the recipient that failed and why.
What it means
A bounce message is written by the server that gave up on the message: the sender's own server when a receiver refused it during SMTP, or a later server that accepted it and then failed to deliver it. It goes to the envelope sender with a null envelope sender of its own, and commonly appears from addresses such as MAILER-DAEMON or postmaster. Most follow the DSN format of RFC 3464, with a readable explanation and a machine-readable report.
For a person, the useful lines are the failed recipient, the reply code, the enhanced status code and the remote server's text. A sending platform receives bounce messages at its bounce address and parses them automatically, often with VERP so that the failed recipient is known from the address alone.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5321, section 6.1: Reliable Delivery and Replies by Emailrfc-editor.org
- RFC 3464: An Extensible Message Format for Delivery Status Notificationsrfc-editor.org
- RFC 3834, section 2: When (not) to send automatic responsesrfc-editor.org
- Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes