550 5.7.1 Our system has detected that this message is likely unsolicited mail
Gmail blocked the message as spam
Seen in Gmail, Google Workspace
Gmail's spam filtering rejected this message outright based on its content, sender reputation or authentication.
Common causes
- Content, links or attachments that look like spam or phishing.
- Poor sender, IP or domain reputation with Gmail.
- Missing or failing SPF, DKIM or DMARC.
How to fix it
- Check SPF, DKIM and DMARC pass and align with the From domain.
- Remove link shorteners, suspicious links and large image-only content, then test again.
- Check reputation and spam rate in Google Postmaster Tools and clean the mailing list.
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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
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- 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
- 421 4.7.26 This mail has been rate limited because it is unauthenticated · Gmail deferred mail that passed neither SPF nor DKIM
- 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