DSN extension
An SMTP extension (RFC 3461) with which a sender asks for delivery status notifications per recipient: on failure, on delay, on success, or never.
What it means
A server that announces DSN accepts four parameters. On RCPT TO, NOTIFY=NEVER, or any combination of SUCCESS, FAILURE and DELAY, says which reports the sender wants for that recipient, and ORCPT records the address as originally given. On MAIL FROM, RET=FULL or RET=HDRS asks for the whole message or only its header in a failure report, and ENVID attaches an identifier that comes back in the report so the sender's software can match it.
Without NOTIFY, a server may act as if NOTIFY=FAILURE or NOTIFY=FAILURE,DELAY had been given, so success reports are never sent unless asked for. They also stop at the first server without DSN support, which reports the message as relayed and nothing more.
Example
RCPT TO:<ana@example.net> NOTIFY=FAILURE,DELAY ORCPT=rfc822;ana@example.netRelated terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
All 432 terms in the glossaryThe wiki: blocklists and bounce codes