What this code means
SPF evaluation for the arriving message resulted in an error, and the system returned a permanent failure. Do not retry the same attempt unchanged.
Technical meaning
The standard X.7.24 pattern denotes an error while SPF is evaluated for an arriving message. It is used instead of 4.4.3 or 5.5.2 in the cases described in Sections 8.6 and 8.7 of RFC 7208. In code 5.7.24, the leading digit assigns the result to the permanent-failure class.
Delivery status
The leading digit 5 denotes a permanent failure of the current attempt. The code does not identify the specific cause of the SPF evaluation error or establish that the recipient 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, controlled attempt only after identifying the cause, making a confirmed correction, and checking suppression again.
Suppression decision
Operational guidance: do not automatically suppress the recipient address or domain based on 5.7.24 alone. Inspect the complete response, event scope, SPF evaluation result, and other delivery signals, then base the suppression decision on the confirmed cause and applicable policy.
Common causes
- SPF evaluation for the arriving message resulted in an error; the code alone does not identify the technical condition that caused it.
Diagnostic steps
- Inspect the raw SMTP response or nondelivery report and confirm the exact 5.7.24 code and a basic reply in the 5xx class; retain the complete response text.
- Correlate the result with the intended message, attempt time and stage, identity used for SPF evaluation, and system that returned the code.
- Use available logs from the SPF-evaluating system and supporting services to establish the actual error; do not infer its cause or responsible party from the code alone.
- Stop unchanged retries. After a confirmed correction, check suppression again and make at most one controlled attempt to verify the result.
Actions by owner
Sender
- Do not manually retry the same unchanged message; confirm that the message and sender identity are intended, then give the sender administrator the complete response and attempt time.
Sender administrator
- Retain the complete response, correlate it with the message and SPF identity, stop unchanged retries, and inspect available sender-side logs and configuration.
- Make only a confirmed correction, check suppression again, and verify the result with one controlled attempt.
Recipient administrator
- If you manage the system that returned the code, inspect its SPF-evaluation and supporting-service logs for the specified attempt; correct a confirmed receiving-side problem or safely give the sender the result needed for remediation.
Provider
- If you operate a managed layer involved in SPF evaluation, inspect its logs and configuration, correct a confirmed problem in that layer or give the appropriate administrators precise diagnostic context, and do not trigger suppression from the code alone.
Sources and verification
The standard meaning of X.7.24, its use for an SPF evaluation error, and its class-5 application were verified against the IANA registry and RFC 2034, RFC 5248, RFC 7208, and RFC 7372 as of July 17, 2026. Diagnostic, remediation, retry, and suppression recommendations are separate operational guidance; this record contains no provider-specific practice.
- iana-smtp-enhanced-status-codesT0 source
Enumerated Status Codes / X.7.24
- 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
- rfc7372T0 source
IANA registry reference for X.7.24
- rfc7208T0 source
IANA registry reference for X.7.24
Last verified:
