Unknown host means, the IP not resolving in the computer/internet connection. Sometimes this may occur if the ISP negatively cached the domainname. Normally this will get released in 4 hours when the ISP DNS refreshes.
you can check the settings yourself from the command prompt.
1) nslookup yourdomainname.com ==> check resolving from your computer dns
2) nslookup yourdomainname.com ns1/ns2.yourdomain-name-server ==> check resolving from your name server dns from the server
3) nslookup yourdomainname.com 220.127.116.11 ==> check resolving from google dns.
If item 2 is resolving the IP, then our serving is correctly working.
if item 3 is resolving the IP, then dns is working with external dns servers also
if item 3 is not resolving, then the problem is with the ISP internet connection.
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