A delivery status notification failure is the receiving mail system's own report explaining why a message did not arrive. RFC 3464 standardizes this report format specifically so a sender's own software, not just a human, can parse the result: which recipient failed, which enhanced status code applies, and which hop in the delivery chain produced the refusal.
Most senders read only the headline, "delivery has failed," and stop there. The report itself carries the actual diagnosis underneath it, in the same enhanced-status-code format (RFC 3463) that a raw 550 or 421 bounce carries.
Every DSN failure names a final recipient address, a status code in the class.subject.detail format, and usually a diagnostic-code line quoting the receiving server's own text. That quoted line is where a policy rejection, a full mailbox, and a bad address stop looking identical.
Searching this exact phrase turns up as much personal-account troubleshooting as sender diagnostics, since the same failure report reaches someone who sent one message from a personal inbox as reaches a business sending at volume. If you are diagnosing your own outbound mail at any real volume, the difference between a soft and a hard bounce is the pattern actually worth reading across many DSN failures, not any single one.
Yes. A DSN failure is the formal report format a mail system generates to describe a bounce, standardized so any receiving system can produce one a sender's software can parse rather than a plain-text message.
This page is written for senders diagnosing their own outbound mail. If you received a DSN failure on a single personal message, the fix is usually confirming the recipient address with the person directly, not a DNS or authentication change.
Most do, since RFC 3464 defines a standard machine-readable format receiving systems widely implement. Some providers instead return a plain-text rejection at the SMTP level with no separate DSN message, which is why the raw enhanced status code matters more than which report format carried it.