TL;DR
Gmail 4.7.24 is a temporary rate limit tied to suspicious SPF-record entries in the accepted example. Correct verified SPF issues, reduce pace, and retry with backoff; do not suppress recipient addresses from this IP-level condition.
What this code means
X.7.24 is registered as a security or policy status detail, and the accepted Gmail response makes the operational scope concrete: suspicious entries in the sending domain's SPF record lead to a temporary rate limit for mail from the sending IP. That evidence does not define behavior at other providers.
Provider examples
451 4.7.24 The SPF record of the sending domain has one or more suspicious entries. To protect our users from spam, email sent from your IP address has been temporarily rate limited. For more information, go to Email sender guidelines. - gsmtpTechnical meaning
RFC 7208 defines SPF evaluation and RFC 7372 registers related enhanced-status usage. Gmail's accepted 451 4.7.24 response specifically says that suspicious entries in the sending domain's SPF record caused temporary rate limiting; it should be read as Gmail-specific response text, not as a universal SPF diagnosis.
Delivery status
Leading digit 4 makes the reported condition temporary. In the accepted Gmail example, the immediate effect is a sending-IP rate limit, not a permanent rejection or proof that a recipient address is bad.
- Class
- Temporary failure
- Retry
- Controlled retry
- Suppression
- Check the full context
Retry decision
Preserve the full Gmail reply, inspect the live SPF record and change history, correct only verified issues, then retry at a reduced pace with backoff, jitter, and a limit. Do not continue at the rate that produced the deferral.
Suppression decision
Do not suppress recipients from 4.7.24 alone. The accepted example is attached to SPF and sending-IP behavior, not to an individual mailbox; use independent permanent recipient evidence for suppression.
Common causes
- The SPF record contains entries Gmail treats as suspicious in the accepted response.
- A recent DNS or ESP change altered SPF structure or authorization unexpectedly.
- Sending continues at a rate unsuitable while Gmail is applying the temporary limit.
Diagnostic steps
- Confirm the full raw Gmail response, including exact 4.7.24 and the 451 basic reply.
- Retrieve and inspect the current SPF record, DNS propagation, include chain, and recent authorized change history.
- Check which sending IP and domain were in use for the failed attempt.
- Correct verified SPF issues, reduce the affected send pace, and use bounded retries.
Actions by owner
Sender
- Pause repeated resends and provide the complete reply, sending domain, and time to the sending administrator.
Sender administrator
- Audit the SPF record and authorized senders, then make controlled DNS changes and pace recovery.
Recipient administrator
- If you manage an inbound policy that affects the result, share safe timing and diagnostic context with the sender.
Provider
- Monitor repeated results by sending IP and domain, validate SPF changes, and apply rate control before resuming volume.
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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