I have SBS2011 network and no one can open this website https://www.kuebix.com
I can open this website from any computer from outside of our network.
in SBS2011 DNS Manager, I don't have any DNS servers listed so that it uses root hints.
We do have a backup DNS server on the same network and each workstation PC has two Name servers: 192.168.1.10 & 192.168.1.11 for example.
Where do I begin troubleshooting this?
No one has reported the same kind of problem before.
These servers should only be caching servers, so your internal lookups match your external lookups.
Be sure you have forwarders setup to either global root servers or better Google's stable servers, which are 126.96.36.199 + 188.8.131.52 + tend to always be up.
Follow becraig's advice. Run an nslookup for your domain explicitly pointing to 184.108.40.206 + then both your Backup DNS Servers.
If there's any difference between what Google (220.127.116.11) returns + your Backup DNS Servers, then best fix this broken config.