X.7.24 · Security or policy
SMTP enhanced status code 5.7.24
SPF validation error
X.7.24 means SPF evaluation itself returned an error, such as a temporary DNS failure (temperror) or a broken record (permerror).
| Registry code | X.7.24 |
|---|---|
| Forms in use | 5.7.24, 4.7.24 |
| Registry name | SPF validation error |
| Subject | 7: Security or policy |
| Permanent or temporary | 4.x.x persistent transient failure: retrying later may succeed; 5.x.x permanent failure: resending unchanged will not succeed |
| Associated basic codes | 451/550 |
| Defined in | [RFC 7372]; [RFC 7208] |
What the registry says
This status code is returned when evaluation of SPF relative to an arriving message resulted in an error. Used in place of 4.4.3 or 5.5.2 as described in [Sections 8.6, 8.7 of RFC 7208].
IANA SMTP Enhanced Status Codes registry, X.7.24
The basic codes it travels with
- 451 Requested action aborted: local error in processing
- 550 Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)
In practice
X.7.24 is an SPF error rather than a fail: the record could not be evaluated. Common causes are syntax errors, more than 10 DNS lookups, and duplicate SPF records. Gmail uses 451 4.7.24 and 550 5.7.24 for SPF records with suspicious entries. A temporary DNS error clears on retry; a broken record needs fixing.
What the sender should do
Check your SPF record for syntax errors and too many DNS lookups; a temporary error usually clears on retry.
Would verifying the list have prevented 5.7.24?
No
This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
How providers use X.7.24
Quoted from each provider’s own error reference.
- Gmail 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.
- Gmail 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.
Common questions
- What does 5.7.24 mean?
- X.7.24 means SPF evaluation itself returned an error, such as a temporary DNS failure (temperror) or a broken record (permerror).
- What is the difference between 5.7.24 and 4.7.24?
- They share the subject and detail digits, so they report the same condition, "SPF validation error". The first digit is the class: 4.x.x persistent transient failure: retrying later may succeed; 5.x.x permanent failure: resending unchanged will not succeed.
- What should I do about 5.7.24?
- Check your SPF record for syntax errors and too many DNS lookups; a temporary error usually clears on retry.
- Would an email verifier have caught 5.7.24?
- No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Sources
- IANA: SMTP Enhanced Status Codes registry (checked 2026-11-05)
- RFC 3463: Enhanced Mail System Status Codes (checked 2026-11-05)
- RFC 5321: Simple Mail Transfer Protocol, section 4.2.3 (reply codes) (checked 2026-11-05)
- Google Workspace Admin Help: Gmail SMTP errors and codes (checked 2026-11-05)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05