- Go to the server that handles your DNS
- Open DNS manager
- Expand the server, Expand the Forward Lookup Zones
- Make sure that you have a zone called: yourdomain.com if not, creating it.
- Expand the zone
- Check to verify that you have a “www” A record and if you’d like add a record without anything (that allows typing http://yourdomain.com without the www) and both should point to your domain’s IP address.
- Propagate the changes to other DNS if they exist and you are done.
- To be on the safe side, right click the server and select Clear Cache.
- Then the clients need to run “ipconfig /flushdns” in cmd line
I would do it in the servers too to check.
You are now done.
Source: [SOLVED] Cannot access company website internally – DNS – Spiceworks