550 5.7.23 SPF validation failed
The message failed the SPF check
Seen in Microsoft 365, Postfix (with SPF policy), various
The sending server isn't authorised in the sender domain's SPF record.
Common causes
- A new sending service not added to SPF.
- SPF exceeds 10 DNS lookups (permerror).
- Mail forwarded through another server.
How to fix it
- Add the service's include or IP to SPF.
- Flatten or trim SPF to stay within 10 lookups.
- Rely on DKIM for forwarded mail.
Got a different message? Paste it into the error explainer.
Related errors
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- 421 4.7.27 Your email has been rate limited because SPF authentication didn't pass for this message · Gmail deferred or blocked mail that failed SPF
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- 550 5.7.25 The IP address sending this message does not have a PTR record · The sending IP has no reverse DNS
- 550 5.1.1 User unknown · The recipient address doesn't exist