Enhanced SMTP status code · RFC 3463 · IANA
5.0.0 Undefined status
The catch-all code, used when only the class of the error (temporary or permanent) is known, not its cause.
- Class: Permanent failure
Class 5: a permanent failure. Resending the same message will not help: something about the message, the sender or the destination must change (RFC 3463 §3.1).
- Subject: X.0 · No specific subject
No additional subject information is available.
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026