Enhanced SMTP status code · RFC 3463 · IANA
5.7.24 SPF validation error
The SPF check ended in an error: temporary (DNS) or permanent (a broken SPF record) (RFC 7372, RFC 7208 §8.6–8.7).
- Class: Permanent failure
Class 5: a permanent failure. Resending the same message will not help: something about the message, the sender or the destination must change (RFC 3463 §3.1).
Also seen as:
4.7.24 - Subject: X.7 · Security and policy
Policies (per-host or per-recipient filters) and cryptographic operations; up to the sender, the recipient or both.
How 5.7.24 appears at providers
The exact text from the provider's documentation, as you see it in the bounce, and what it means.
Gmail
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550 5.7.24
The SPF record of the sending domain has one or more suspicious entries.
Gmail finds one or more entries of the sending domain's SPF suspicious, so it limits or blocks the mail. Review every mechanism in the SPF record. Check with SPF generator.
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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.
Gmail finds one or more entries of the sending domain's SPF suspicious, so it limits or blocks the mail. Review every mechanism in the SPF record. Check with SPF generator.
What you can check here
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026