exchange-mx.netnames.com has no NS records.
NS records for this zone are defined at netnames.com.
NS records for this zone are defined at netnames.com.
Question and response
Question
dig exchange-mx.netnames.com. NS
Answer
The response has no answer records.
Authority
netnames.com. 21600 SOA udns1.cscdns.net. hostmaster.cscdns.net. 2017101358 3600 1800 3600000 21600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0