Exact response pattern
550 5.5.3 Too many recipientsPermanentGenericRate limit
What it means
The receiver permanently rejects the transaction because it has too many recipients.
Likely causes
- Batch size exceeds policy.
Recommended response
- Split the recipient list into smaller transactions.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.