What this code means
The system permanently refused the message because the sender was not authorized to send to the intended mailing list. Do not retry the same unchanged attempt.
Technical meaning
The X.7.2 pattern means that the sender is not authorized to send a message to the intended mailing list. The standard says this detail is useful only as a permanent error, and code 5.7.2 applies it in class 5.
Delivery status
The leading digit 5 denotes a permanent failure of the current attempt. The code describes an authorization refusal for a list, but by itself it does not identify the specific rule or establish that the list address is invalid.
- Class
- Permanent failure
- Retry
- Do not retry unchanged
- Suppression
- Check the full context
Retry decision
Operational guidance: stop automatic and manual retries of the same unchanged attempt. Consider a new send only after a verified change to the sender identity, its authorization, or the applicable list rule; check suppression again before the attempt.
Suppression decision
Operational guidance: do not automatically add the list address or domain to a suppression list based on 5.7.2 alone. Inspect the complete response, list-authorization context, event history, and applicable policy, then make the suppression decision in that context.
Common causes
- The system serving the intended mailing list determined that the sender was not authorized to send a message to it.
Diagnostic steps
- Inspect the raw SMTP response or nondelivery report and confirm that the enhanced code is exactly 5.7.2 and that the basic reply is in the 5xx class; retain the complete response text.
- Correlate the event with the intended message, attempt time, sender identity used, intended list, transaction stage, and system that returned the code; identify the applied rule from available logs instead of inferring it from the code alone.
- Stop unchanged retries; before a controlled new send, verify a material change to authorization, identity, or the list rule and check suppression again.
Actions by owner
Sender
- Do not resend the same unchanged message; confirm the intended sender identity and list, then give the administrator the complete response.
Sender administrator
- Retain the complete response and attempt context, inspect the sender identity and sending-path configuration used, and coordinate with the list administrator to identify the authorization that requires correction.
Recipient administrator
- If you manage the list, inspect the posting rules and sender authorization applied to the specified attempt; correct them only if they do not match the intended policy.
Provider
- If you operate a system involved in the attempt, inspect managed-service logs and the applied rule, then give the administrators safe context needed to verify the appropriate correction.
Sources and verification
The standard X.7.2 meaning and its use only as a permanent error were verified against the IANA registry and RFC 2034, RFC 3463, and RFC 5248 as of July 17, 2026. Diagnostic, remediation, retry, and suppression recommendations are separate operational guidance.
- iana-smtp-enhanced-status-codesT0 source
Enumerated Status Codes / X.7.2
- 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.7.2
Last verified:
