Are you planning on running your own domain name servers? I'm not a fan of doing that myself when I can depend on my registrar who will have a far more robust set up. I realize I am not as expert as others here, but this is some of the things I would try...
1 - make sure my DNS server is set up correctly and has propagated. I would use my registrar because this takes out a misconfiguration locally for the time being. Again, their servers will be more robust and you save resources too by not running your own DNS.
2- Use MXToolbox to see if there is anything misconfigured, those tools will also tell you if they cannot reach the site
3 - See if you can reach your server from another IP (like your phone's) I also think you can SSH using putty using a domain name too.
4 - If you're not able to reach the site, a firewall misconfiguration is the first candidate to check. I'm guessing you opened all of the ports DA recommends (I see you posted to that information earlier)
5 - Are you running any other firewall program? I run on Google Cloud and I had to open ports there, on the server itself and also in CSF (which I run). In your case you'd also need to check the router.