Exact response pattern
523 5.3.4 Message too largePermanentGenericContent
What it means
The server refuses the message because it exceeds the size limit.
Likely causes
- Attachments or MIME overhead.
Recommended response
- Reduce size and send a new message.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.