because it simple...

lookup dns records of domain,fetch dns records

Main content page - fetch dns records.The NS lookup test performs an NS record (Name Servers record) lookup for a specific domain name, which returns the Name Servers responsible for the domain name records. The test results display the hostnames and IP addresses of the Name Servers.
From there I do a reverse DNS (rDNS) lookup to see what hostname the ISP provides. A hostname is something like www.example.com, or can be more specific to include regional information.
Because IMAP UIDs are assigned in this manner, to retrieve new messages an IMAP client need only request the UIDs greater than the highest UID among all previously-retrieved messages, whereas a POP client must fetch the entire UIDL map.
There are a number of ways to find out whether your system is resolving properly. You can use nslookup to verify name resolution. The nslookup command can be used to find various details relating to a particular DNS (Domain Name System) such as IP address, MX records etc.
Without DNS in action no website can operate online. Websites are connected with DNS through certain DNS settings assigned to their domain names by their registrars/hosts. Each domain name registered with NTC Hosting comes with a set of options for full DNS Management such as NS Records, Custom A&MX Records, CNAME Records, AAAA Records, TXT Records, etc.