RFC 3463 / START HERE
Enhanced mail status, before the details
Enhanced Mail System Status Codes names a code format, not an expanded acronym.
A dotted code such as 4.2.2 describes a mail delivery condition using three fields: outcome class, problem subject and specific detail. A Delivery Status Notification (DSN) is a structured report about what happened to mail; the code helps software explain it consistently across languages.
The idea in one picture
Mail status
Read three fields
Explain the outcome
A simplified picture of the idea; the chapters explain the actual mechanisms.
Why it exists
Ordinary SMTP reply numbers and free-form text do not give enough structured detail for delivery reports. RFC 3463 separates mailbox, system, routing, content and policy conditions. Later updates add definitions and registry rules; this is the foundational code model rather than a complete current registry.
A familiar example
When a fictional recipient’s mailbox is full, a report might use 4.2.2. A reader can distinguish a temporary storage condition from a bad address, and still report the broad class when a detail is unfamiliar. Codes do not prescribe a retry schedule, prove that a diagnosis is true or authenticate a sender.
Helpful background
You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.
What you’ll learn next
Begin with chapter one, or choose a topic.
- Read the three fields without inventing a new SMTP codeAn enhanced status code is a dotted class, subject and detail. It describes a mail-system condition; it is not a replacement spelling for an ordinary three-digit SMTP reply.→
- Distinguish success, temporary conditions and permanent failureThe leading field carries the broad outcome even when a reader does not know the rest. It guides interpretation rather than specifying an automatic retry schedule.→
- Locate the cause with the subject and detail togetherA repeated detail number can mean different things under different subjects. Compare an address error, a mailbox condition and a system-wide storage condition.→
- Preserve what is known when a detail is unfamiliarA reader may encounter a well-formed code whose specific detail or subject it does not recognize. Report the broader meaning that remains known.→
- Use the registry and limit what a diagnostic revealsLater documents add codes and registry rules. Consult the referenced definition rather than guessing from number shape, and remember that precise diagnostics can expose internal details.→
This introduction explains RFC 3463 (2003). Read the original RFC ↗