451 4.7.26: DMARC check hit a DNS failure
Gmail could not finish checking SPF and DKIM because a DNS lookup failed, and the From domain's DMARC policy says to reject mail that does not authenticate.
- Gmail
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 451 4.7.26
- Provider
- Gmail and Google Workspace
- Temporary or permanent
- TemporaryThe sending server keeps the message and tries again later.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
451 4.7.26 …not accepted due to domain's DMARC policy, but temporary DNS failures prevent authentication.
What it means
The domain in the From address publishes a DMARC policy that asks receivers to refuse mail that fails authentication, so Gmail must confirm that the message passes SPF or DKIM in alignment with it. While checking, a DNS lookup failed, so authentication could not be confirmed either way. Instead of rejecting mail that may be legitimate, Gmail defers it with this temporary code and expects a retry. If the DNS trouble is brief, a later attempt passes. If it keeps happening, look at the DNS servers for the From domain, the DKIM selector record and each SPF include, since any slow or broken one can cause it.
Common causes
- Slow or failing authoritative DNS servers for the sending domain.
- A DKIM selector record or SPF include hosted on a DNS service that timed out.
- An SPF record that needs many nested lookups, any of which can fail.
How to fix it
- 01Let the message retry; a short DNS outage clears on its own.
- 02Test your domain's DNS servers for timeouts and make sure all of them answer for the zone.
- 03Check that the DKIM selector record and each SPF include resolve quickly from outside your network.
- 04Reduce SPF lookups by removing includes you no longer need.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Gmail SMTP errors and codes (Google Workspace Admin Help)knowledge.workspace.google.com
Related codes
- 550 5.7.26Rejected under the sender's DMARC policy.Gmail rejected the message because it failed DMARC, and the From domain's DMARC policy tells receivers to refuse mail that fails.
- 451Local error in processing.The receiving server hit a problem on its own side while handling the message and stopped. The reply is temporary, so the sending server will try again.
- 550 5.7.26Multiple authentication checks failed.The message failed more than one authentication check, for example SPF and DKIM, and the receiving server's policy rejects it.
4.7.26 at other providers
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce