You want to know what DNS Recursion is and when it's appropriate to use that feature with the ProxySG appliance.
Non-recursive means that a DNS server can provide a partial answer or return an error to the client.
Recursive means that the DNS server either fully answers the query or returns an error to the client
ProxySG Appliance Using Non-Recursive DNS
If you have defined more than one DNS server, the ProxySG appliance uses the following logic to determine which servers are used to resolve a DNS host name and when to return an error to the client.
Note: Servers are always contacted in the order in which they appear in a group list.
The ProxySG appliance first checks all the DNS groups for a domain match, using domain-suffix matching to match a request to a group.