Infrastructure
What is DNS resolver?
The service that turns names into addresses. Its logs record which names machines on your network asked for.
A DNS resolver is the service that turns a name such as example.com into an IP address on behalf of the machines that ask. Every outbound connection by name starts with a resolver query.
That makes resolver logs one of the most useful sources an organisation owns. They show which internal host asked for which domain and when, which is often enough to confirm whether a malicious domain from a threat report was ever contacted.