The source of truth for a zone
An authoritative server serves records exactly as the domain administrator wrote them: A, MX, TXT and others. The start of the zone is described by the SOA record, which names the primary server, the administrator contact and the refresh parameters. An authoritative server never invents an answer or asks anyone else: it either knows the record or honestly reports that the name does not exist.
Authoritative versus recursive
The two roles are easy to confuse, but they do different jobs:
- Authoritative — holds the genuine zone data and gives the final answer from it.
- Recursive — a recursive resolver stores no zones itself; it walks the hierarchy and caches other servers' answers.
- Delegation — which server is authoritative for a domain is set by its NS records in the parent zone.
When a resolver reaches a domain's authoritative server, the lookup ends: there is no one further to ask.
