What this code means
The receiving system permanently rejected the message and indicated that the owner of the recipient's domain had changed since the time supplied through RRVS. Do not retry the same unchanged attempt.
Technical meaning
The X.7.18 pattern is returned when a message contains a Require-Recipient-Valid-Since field or RRVS extension and the receiving system wishes to disclose that the owner of the recipient's domain has changed since the specified time. In code 5.7.18, the leading digit assigns the result to the permanent class.
Delivery status
The leading digit 5 denotes a permanent failure of the current attempt. The code alone identifies neither the previous nor current domain owner and does not state why the ownership changed.
- 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, controlled attempt only after verifying the recipient, domain, and RRVS context and confirming a material correction; check suppression again first.
Suppression decision
Operational guidance: do not automatically add the address or domain to a suppression list based on 5.7.18 alone. Inspect the complete response, RRVS context, domain-ownership change, and other delivery events, then make the suppression decision according to the confirmed cause and applicable policy.
Common causes
- The message contained a Require-Recipient-Valid-Since field or RRVS extension, and the receiving system determined that the owner of the recipient's domain had changed since the specified time.
Diagnostic steps
- Inspect the raw SMTP response or nondelivery report and confirm the exact 5.7.18 code and a basic reply in the 5xx class; retain the complete response text.
- Correlate the event with the intended message, attempt time and stage, recipient domain, and time supplied in the Require-Recipient-Valid-Since field or RRVS extension; do not infer the owners' identities from the code alone.
- Ask the receiving-system administrator or provider to inspect available logs and confirm the domain-ownership-change condition. Stop unchanged attempts and check suppression before any new, controlled send after a confirmed correction.
Actions by owner
Sender
- Do not resend the same unchanged message; confirm the intended recipient and domain, then give the sender administrator the complete response.
Sender administrator
- Retain the complete response and attempt context, verify the recipient domain and RRVS time used, stop unchanged retries, and coordinate a confirmed correction with the recipient administrator or provider.
Recipient administrator
- If you manage the system that returned the code, inspect its logs for the specified domain and RRVS time, confirm the domain-ownership-change condition, and give the sender safe context needed for the next decision.
Provider
- If you operate a system involved in the attempt, inspect managed-service logs and RRVS context, confirm the basis of the result, and do not trigger suppression based on the code alone.
Sources and verification
The canonical meaning of X.7.18 and its class-5 application were verified against the IANA registry, RFC 2034, RFC 5248, and RFC 7293 as of July 17, 2026. Retry, suppression, diagnostic, and owner-action guidance is presented separately as operational advice; this record contains no provider-specific practice.
- iana-smtp-enhanced-status-codesT0 source
Enumerated Status Codes / X.7.18
- 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
- rfc7293T0 source
IANA registry reference for X.7.18
Last verified:
