Exact response pattern
530 5.7.1 Client was not authenticatedPermanentGenericAuthentication
What it means
The action requires an authenticated SMTP session.
Likely causes
- AUTH missing or failed.
Recommended response
- Authenticate over TLS with valid credentials.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.