What this code means
Code 5.0.0 is a general permanent failure: only class 5 is known, with no more specific status. Do not retry the same unchanged attempt.
Technical meaning
The X.0.0 pattern is the only undefined status code and is used when only the result class is known. In the 5.0.0 variant, that result class is permanent failure.
Delivery status
This is a permanent status, not a temporary error. The code alone does not identify the exact cause or establish that the recipient address is the problem.
- Class
- Permanent failure
- Retry
- Do not retry unchanged
- Suppression
- Check the full context
Retry decision
Do not retry an unchanged attempt after code 5.0.0. Before any new submission, determine the cause from the full response and change the relevant data, configuration, or handling.
Suppression decision
Do not apply automatic blanket suppression based on code 5.0.0 alone. Inspect the full response, context, and other permanent signals, then decide according to the established cause and applicable policy.
Common causes
- Only the permanent-failure class is known, so the general 5.0.0 code is used.
- The exact reason remains unspecified; code 5.0.0 itself provides no more specific status.
Diagnostic steps
- Inspect the raw SMTP transaction response or delivery report and confirm that it contains the exact enhanced code 5.0.0.
- Confirm that the basic SMTP reply is in the 5xx class and agrees with the enhanced 5.x.x class; note the SMTP stage and accompanying text.
- Trace response mapping in logs and webhooks to determine whether a more specific status was lost or normalized to 5.0.0.
Actions by owner
Sender administrator
- Stop retrying the unchanged attempt and retain the full raw response for investigation.
- Establish the cause before a new submission; base suppression on the full context and policy, not solely on code 5.0.0.
Provider
- Retain the full raw SMTP response and a more specific status code when one is available.
- Review normalization rules when available permanent-failure detail is replaced by the general 5.0.0 code.
Sources and verification
The standard meaning and class assignment were verified against the IANA registry and RFC 2034, RFC 3463, and RFC 5248. The absence of an accepted Tier-1 example describes provider-data coverage only. Retry, suppression, diagnostics, and owner actions are operational guidance, not facts asserted by the standards or any specific provider.
- iana-smtp-enhanced-status-codesT0 source
Enumerated Status Codes / X.0.0
- rfc5248T0 source
Section 2.1: registry fields and non-exclusive Associated Basic Status Code
- rfc2034T0 source
Section 4: enhanced status class agrees with SMTP reply class
- rfc3463T0 source
IANA registry reference for X.0.0
Last verified:
