I ran into an issue installing a new build of Exchange 2016 CU3 on Windows 2012 R2. I’m not sure how the Servers were built. I had to scrap the previous attempted installation from another consulting firm. I fear these Servers were just reverted to a pre-Exchange snapshot but I was told otherwise. In any event, upon the first 2 servers installation I was given a warning from the installer “The primary DNS server cannot be contacted_PrimaryDNSTestFailed”. After doing research, I’ve seen this issue has happened back as far as Exchange 2007. The customer is using a non Windows DNS configuration, I’m not sure if that exactly plays a role or not. The fix was to join the Server back to a workgroup, then join it back to the domain. This is a pretty common fix for a host of various errors. Not too much to it, but wanted to put it out there if it could help someone!