What lookup tools report.
NXDOMAIN
The domain does not exist, according to the authoritative nameservers.
Either it is not registered, has expired, or the name is wrong.
For a subdomain, it means no record exists for that name.
SERVFAIL
The nameserver failed to answer. Something is wrong at the server or in the chain.
Frequently a DNSSEC validation failure, which produces exactly this.
REFUSED
The nameserver declined to answer for that domain. Usually it is not authoritative for it.
Common when nameservers were changed and the old provider no longer holds a zone.
NO ANSWER
The query succeeded and no record of that type exists.
A lookup for MX records returning no answer means no MX records exist, which is why mail is failing.
TIMEOUT
The nameserver did not respond. Either it is unreachable or the query was blocked.
WHICH MATTER MOST
- NXDOMAIN for a domain that should exist: check registration and expiry.
- No answer for MX records: mail records missing.
- SERVFAIL: check DNSSEC.
