SMTP code 5.X.X
What the knowledge base's own tables say about this code, and which articles say it — a description of the reply, never a placement prediction.
- Meaning
- Permanent failure: resending the message in its current form is not likely to resolve it
- Next step
- Hard bounce: do not retry unchanged, and suppress the address when the cause concerns the address
From SMTP Enhanced Status Codes (RFC 3463) · Class (first number): is it permanent?