Internal resolution domain hosts on Fortigate

Hi,

how could I configure FGT to resolve my all domain hosts, but only for its internal purposes I mean FGT should know hot co access to my mail.ad.company.com and sms gateway like sms.ad.company.com. Now fortigate because of Fortiguard DNS configured, retrieve this hosts from internet side. I don't want to run DNS server on any LAN facing interfaces, because all clients get IP of my domain AD DNS already.