Exact response pattern
550 5.1.0 Address rejectedPermanentGenericRecipient
What it means
The envelope address was rejected permanently.
Likely causes
- Invalid address syntax.
- Recipient policy.
- Unknown local routing.
Recommended response
- Validate the address.
- Remove it after confirming a permanent recipient failure.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.