Accesing an external server with a pure domain name

I have a server on the internet with the name, say, “example.org” and my UCS domain is also “example.org”. Inner servers, with UCS have names srv1.example.org, srv2.example.org etc. Before upgrading to UCS 5.0 I could reach my external server via example.org, now DNS server on UCS on request for IP of example.org gives an IP of the domain controller.
How to set up it, so for the IP of example.org UCS DNS will again request an external DNS server?