421 4.7.26 This mail has been rate limited because it is unauthenticated
Gmail deferred mail that passed neither SPF nor DKIM
Seen in Gmail, Google Workspace
Gmail requires every sender to pass SPF or DKIM; this message passed neither, so Gmail deferred it (repeated failures become a 550 5.7.26 rejection).
Common causes
- The sending server is not listed in SPF and does not sign with DKIM.
- DKIM signing is set up but the public key is not published in DNS.
- A 451 4.7.26 variant means DMARC could not be checked because of a temporary DNS failure.
How to fix it
- Add the sending service to SPF and enable DKIM signing with your domain.
- Publish the DKIM public key at selector._domainkey.example.com and confirm it resolves.
- Check the message headers for the SPF and DKIM results Gmail recorded.
Got a different message? Paste it into the error explainer.
Related errors
- 550 5.7.26 Unauthenticated email is not accepted · Gmail rejected mail that failed DMARC
- 550 5.7.1 Relaying denied / Message rejected · The receiving server refused the message on policy grounds
- 421 4.7.0 Try again later · Temporarily deferred by the receiving server
- 550 5.7.515 Access denied, sending domain does not meet the required authentication level · Outlook.com rejected unauthenticated bulk mail
- 550 5.7.23 SPF validation failed · The message failed the SPF check
- 550 5.7.509 Access denied, sending domain does not pass DMARC verification and has a DMARC policy of reject · Microsoft 365 rejected mail that failed DMARC
- 421 4.7.28 Our system has detected an unusual rate of unsolicited mail originating from your IP address · Gmail is rate limiting mail from your IP
- 550 5.7.1 Our system has detected that this message is likely unsolicited mail · Gmail blocked the message as spam
- 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
- 421 4.7.0 [TSS04] Messages from x.x.x.x temporarily deferred due to unexpected volume or user complaints · Yahoo is temporarily deferring your mail
- 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