To clarify, the Ecessa appliance does not behave as an internal DNS server - it's purpose as a DNS server is to provide inbound load balancing and redundancy by dynamically updating answers to external DNS requests based on WAN link availability. However, it may resolve publicly available hostnames for LAN users by forwarding the requests to other servers.
To accomplish this, the Ecessa appliance must be configured as the DHCP server for the LAN it is to serve as a DNS server.
Additionally, the Recursive Resolver setting must be enabled. When enabled, the Ecessa unit will provide its own address as the DNS name server for DHCP clients. To answer DNS requests, it will use the DNS name servers configured in the DHCP section as forwarders. If no DNS name servers are specified on the LAN configuration page, the unit will use the DNS resolver addresses specified on the Services configuration page.
Note: by default the Primary DNS resolver address is 127.0.0.1 which will prevent DNS resolution from working properly if no other DNS servers are configured.
Even if a domain is locally configured on the Ecessa appliance (such as example.com), it will always forward the request to the configured DNS forwarders.