TL;DR
Permanent failure: SPF evaluation itself errored on the incoming message. Fix DNS, SPF configuration, or resolver issues before retrying. Authentication infrastructure faults can indirectly affect deliverability. Do not retry unchanged.
What this code means
Lookup or infrastructure faults during SPF for an arriving message map to registry pattern X.7.24 as code 5.7.24 when evaluation ends in error rather than pass, fail, neutral, or softfail. RFC 7208 Sections 8.6 and 8.7 prescribe this code instead of 4.4.3 or 5.5.2 in those cases, and class 5 assigns a permanent refusal. The detail is not an SPF policy verdict. It does not name a DNS timeout, malformed record, resolver failure, or which component failed; diagnosis still needs SPF evaluation logs and supporting service traces.
Provider examples
550 5.7.24 The SPF record of the sending domain has one or more suspicious entries. For more information, go to Email sender guidelines. - gsmtpTechnical meaning
An error while SPF is evaluated for an arriving message is denoted by X.7.24. Operators use it instead of 4.4.3 or 5.5.2 in the cases described in Sections 8.6 and 8.7 of RFC 7208. Code 5.7.24 assigns the result to the permanent-failure class through its leading digit.
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
These sources define what this enhanced status code means, mainly through the IANA registry and related RFCs. When provider examples appear on the page, they come from that provider's published documentation. Follow the links to read the original wording in context.
- SMTP Enhanced Status Codes — IANA registry of enhanced mail system status codes.
- RFC 5248 — A Registry for SMTP Enhanced Mail System Status Codes — Creates and governs the IANA enhanced status code registry.
- RFC 2034 — SMTP Service Extension for Returning Enhanced Error Codes — Defines how SMTP returns enhanced status codes to clients.
- RFC 7372 — Email Authentication Status Codes — Status codes for SPF, DKIM, DMARC and related authentication results.
- RFC 7208 — Sender Policy Framework (SPF) — SPF standard for authorizing domains that send mail.
- Gmail SMTP errors and codes — Official Gmail Help table of SMTP error messages and status codes.
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