Exact response pattern
550 5.6.0 Message content errorPermanentGenericContent
What it means
The message content or MIME structure cannot be processed.
Likely causes
- Malformed MIME.
- Broken encoding.
Recommended response
- Validate message generation and MIME boundaries.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.