SERVFAIL
The DNS response code (RCODE 2) meaning the server could not process the query because of a problem on its side or further upstream.
What it means
A resolver returns SERVFAIL when it cannot get a usable answer: the authoritative servers are unreachable or broken, they return inconsistent data, or DNSSEC validation failed. Unlike NXDOMAIN, it says nothing about whether the name exists.
For mail this produces temporary failures: SPF temperror, DMARC checks that cannot finish, and senders that defer delivery because MX lookups fail. Gmail, for example, defers with 451 4.7.26 when its DMARC check hits a DNS failure.
Persistent SERVFAIL for a domain often points to its DNS host or to a broken DNSSEC chain after a change of provider.
Related terms
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Sources
What this definition rests on. The wording is ours; the facts are theirs.
All 432 terms in the glossaryThe wiki: blocklists and bounce codes