5.7.25SMTP 5.7.25: Reverse DNS validation failed

Reverse DNS validation failed for the SMTP client's IP address against the receiving system's local policy; that outcome is registry pattern X.7.25, returned as code 5.7.25. Permanent-failure class 5 in the enhanced status register frames the result for this attempt. The subcode names a policy-layer rDNS gap rather than a specific DNS misconfiguration on the client path. The code alone does not show whether the PTR record is missing, stale, or mismatched, nor which hop enforces the check.

Reverse DNS validation failure for an SMTP client's IP address, contrary to local policy requirements, matches X.7.25. Code 5.7.25 applies that meaning in the permanent-failure class for this check.

The leading digit 5 denotes a permanent failure of the current attempt. The code does not establish why reverse DNS validation failed, which layer needs correction, or the policy of any particular provider.

Class

Permanent failure

Retry

Do not retry unchanged

Suppression

Check the full context

Operational guidance: stop automatic and manual retries of the same unchanged attempt. Consider a new, controlled attempt only after establishing the cause, making a confirmed correction, and checking the reverse DNS result; check suppression again first.

Operational guidance: do not automatically suppress the recipient address or domain based on 5.7.25 alone. Inspect the complete response, event scope, DNS results, available logs, and delivery history, then base the suppression decision on the confirmed cause and applicable policy.

• The SMTP client's IP address failed the reverse DNS check required by the local policy of the system that returned the code; the code alone does not identify the exact reason validation failed.

1. Inspect the raw SMTP response or nondelivery report and confirm the exact 5.7.25 code and a basic reply in the 5xx class; retain the complete response text.
2. Correlate the response with the intended message, attempt time and stage, SMTP client IP address, and system that returned the code.
3. Use available logs, DNS results, and local-policy configuration to establish which reverse DNS check failed and why; do not assign a specific cause or provider practice from the code alone.
4. Stop unchanged retries. After a confirmed correction, check the reverse DNS result and suppression again, then make at most one controlled attempt.