I'm configuring the SMTP service on a new Windows Server 2016 build. I've installed the required software, accessed the Admin tool and set up access and relay control.
This server will just be handling outbound mail for status messages from printers, backup systems, etc. There will be no mail coming in from outside the network.
I'm trying to set up the ISP's mail relay as a smart host, but I'm having trouble. I've entered the fully qualified domain name for the server, left the Masquerade name blank, and added the IP address of the smart host (The address I've used is the address of a known SMTP relay on my test network. It will change in production)
The problem is this: if I click the Check DNS button I get a message saying the domain name is valid. If I then click the OK button, I get a message saying the domain name is not valid.
What have I missed?