550 5.7.26 Unauthenticated email is not accepted
Gmail rejected mail that failed DMARC
Seen in Gmail bounces
The message failed SPF and DKIM alignment, and the sender's domain has a DMARC policy (or Gmail's bulk-sender rules apply).
Common causes
- Sending through a service not listed in SPF and not signing with your domain's DKIM key.
- Forwarding that breaks SPF without DKIM.
- A DMARC record with p=reject while some legitimate senders aren't authenticated.
How to fix it
- Add the sending service to SPF and enable DKIM signing with your domain.
- Use DMARC reports to find unauthenticated sources.
- Make sure the From domain aligns with the SPF or DKIM domain.
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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