NXDOMAIN
The DNS response code (RCODE 3) meaning the queried name does not exist at all, with no records of any type.
What it means
RFC 1035 calls it Name Error; NXDOMAIN is the usual name. It is different from NODATA, where the name exists but has no record of the type asked for.
In mail it shows up in several ways. Senders bounce mail to a domain that returns NXDOMAIN. SPF counts it as a void lookup. DMARC defines non-existent subdomains by it, which is what np= targets. And a DNS blocklist publishes no records for an address it does not list, so checking a clean address returns NXDOMAIN.
Negative answers are cached according to the zone's SOA record, so a name created just after someone queried it can stay invisible for a while.
Related terms
On this site
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