451 Yahoo bounce: dns lookup failed, retry
What 451 means
Yahoo could not complete a DNS lookup for your sending domain, so it deferred the message with 451.
Message text
DNS-related failures can be returned as either a timeout/servfail (451) or a permfail (554).
Common causes of 451
- MAIL FROM or header From domain has no SOA record
- MAIL FROM or header From domain has no A or MX record
- DNS timeout or SERVFAIL from the sending domain's name servers
How to fix 451
- Confirm the MAIL FROM and From domains have SOA and A or MX records with MX lookup.
- Make sure your authoritative DNS servers answer reliably.
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How to read 451
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).
This reply carries no enhanced status code. The three-digit reply code is the only machine-readable signal, so read the text that follows it to learn the reason.
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: senders.yahooinc.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
FAQ
What does 451 mean?
Yahoo could not complete a DNS lookup for your sending domain, so it deferred the message with 451. This is a temporary failure.
How do I fix 451?
Confirm the MAIL FROM and From domains have SOA and A or MX records with MX lookup. Make sure your authoritative DNS servers answer reliably.
Is 451 permanent, and should I retry?
451 is a temporary failure. Your mail server normally retries by itself; if it keeps repeating, fix the cause.