DSN (Delivery Status Notification)
Also called: bounce message, NDR, non-delivery report
A structured MIME report generated by a mail transfer agent describing the result of an attempt to deliver a message to one or more recipients. It is the machine-readable format behind what users see as a bounce message.
In plain terms
The formal, parseable version of the 'your message could not be delivered' email.
Why it matters for deliverability
DSNs are what makes automated bounce handling possible. Parsing the structured report gives you the recipient, the status code and the reporting server; scraping the human-readable text gives you a guess.
What to do about it
- Parse the message/delivery-status part rather than the human-readable body.
- Key your suppression logic on the enhanced status code inside the DSN.
- Make sure your Return-Path points somewhere you actually process, or the DSNs go nowhere.
Source
RFC 3464 — An Extensible Message Format for Delivery Status Notifications
“a Multipurpose Internet Mail Extensions (MIME) content-type that may be used by a message transfer agent (MTA) ... to report the result of an attempt to deliver a message”
Checked 2026-08-29
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Definitions reviewed 2026-08-29. Spotted something wrong? Tell us.
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