In relation to caching DNS servers it is necessary to inform clients whether the response that is sent to them, came from caching server or directly from an authoritative DNS server. For this is used the flag in the message header of the DNS protocol. As nonauthoritative is marked also the response, which at this moment caching DNS server, has received from the relevant authoritative server. As authoritative is marked only one that we get directly without any mediation.
At this point, it should be stressed again that the flag of an authoritative response does not mean that the domain is actually delegated to the DNS server. The point is that the domain administrator added domain to the server and created a zone for it. The server does not verify if they have really delegated domain. There can occur a problem that is described in the section „Recursive and non-recursive requests“.