What is a Delivery Status Notification (DSN)?
A Delivery Status Notification is a machine-readable report about message delivery. It can report failure, delay, successful delivery, relay, or address expansion—and it normally includes one block of fields for each affected recipient.
Updated July 15, 2026
The fields that matter
| Field | What it tells you |
|---|---|
| Final-Recipient | The address used for the final delivery attempt |
| Action | failed, delayed, delivered, relayed, or expanded |
| Status | The enhanced X.Y.Z result |
| Remote-MTA | The remote mail system involved |
| Diagnostic-Code | The SMTP reply and human/provider detail |
The human-readable top of a bounce is convenient, but these structured fields are safer for automation. A multi-recipient message can succeed for one address and fail for another.
A minimal failure example
Final-Recipient: rfc822; user@example.com
Action: failed
Status: 5.1.1
Remote-MTA: dns; mx.example.com
Diagnostic-Code: smtp; 550 5.1.1 User unknownAction: failed and status class 5 make this permanent. The 1.1 detail and diagnostic text identify the recipient address as the problem.
DSNs can contain sensitive data
A report can include recipient addresses, server hostnames, message identifiers, and part or all of the original message. Redact personal and message content before posting a DSN publicly or sending it to a third party.
What a DSN does not prove
A successful delivery status means the receiving system accepted the message at the reported stage. It does not prove that a human read it, that it landed in the inbox rather than spam, or that a later mailbox rule did not move it.