451 4.7.26 Gmail bounce: dmarc lookup failed
What 451 4.7.26 means
Gmail could not finish the DMARC check because DNS lookups failed temporarily, so it deferred the message instead of accepting or refusing it.
Message text
Unauthenticated email from domain-name is not accepted due to domain's DMARC policy, but…
This is an excerpt: the provider's documentation shortens the message. Full text: provider documentation
Common causes of 451 4.7.26
- Temporary DNS failure while looking up the DMARC or SPF/DKIM records
- Authoritative DNS server for the sending domain did not answer
How to fix 451 4.7.26
- Check that the _dmarc record exists and answers with DMARC checker.
- Make sure the sending domain's DNS servers answer reliably; the message will normally deliver on retry.
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How to read 451 4.7.26
The first part, 451, is the SMTP reply code. Requested action aborted, local error in processing: the server hit a problem and did not finish the command. Replies that start with 4 are temporary and replies that start with 5 are permanent (RFC 5321 §4.2.1).
The second part, 4.7.26, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 4 is a Persistent transient failure (4xx): the command was not accepted, but the condition may clear, so the sender should try again later (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 7 is security or policy: authentication, authorization or policy refused the message. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.
Sending servers should retry a deferred message. RFC 5321 §4.5.4.1 advises waiting at least 30 minutes between attempts and trying for at least 4 to 5 days before giving up and returning a bounce. If the deferral keeps repeating, fix the cause rather than waiting.
Official source: knowledge.workspace.google.com. Last verified 2026-10-20.
Related guides
- How to create an SPF record (syntax and examples)
- How DKIM works and how to publish a DKIM record
- How to set up a DMARC record, from p=none to p=reject
Related codes
- 4.7.26 Microsoft: ipv6 needs spf or dkim
- 421 4.7.26 Gmail: unauthenticated rate limit
- 4.7.0 SMTP: security status
- 421 4.7.0 Gmail: no PTR record
- 451 4.7.23 Gmail: PTR record missing
- 421 4.7.28 Gmail: rate limited
FAQ
What does 451 4.7.26 mean?
Gmail could not finish the DMARC check because DNS lookups failed temporarily, so it deferred the message instead of accepting or refusing it. This is a temporary failure.
How do I fix 451 4.7.26?
Check that the _dmarc record exists and answers with DMARC checker. Make sure the sending domain's DNS servers answer reliably; the message will normally deliver on retry.
Is 451 4.7.26 permanent, and should I retry?
451 4.7.26 is a temporary failure. Your mail server normally retries by itself; if it keeps repeating, fix the cause.