Exact response pattern
550 5.1.8 Bad sender system addressPermanentGenericSender
What it means
The envelope sender domain or address is invalid.
Likely causes
- Invalid MAIL FROM domain.
- Missing DNS.
- Malformed bounce address.
Recommended response
- Use a valid envelope-from domain.
- Publish required DNS and ensure the address syntax is correct.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.