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Error codes

550 5.7.40 Your message was blocked because the sending domain doesn't have a DMARC record or the DMARC record doesn't specify a DMARC policy.

Gmail blocked the message because the sending domain has no DMARC record, or the record has no policy. Bulk senders have to publish DMARC.

  • 421 4.7.40 is the rate-limited twin of the same missing-record or missing-policy case.

The title is the 550 5.7.40 row on Google's SMTP error list, last updated 18 September 2026 UTC. RFC 7489 requires v and p on a policy record. none, quarantine, and reject are the three p values.