mx1.nctc.com has no NS records.
NS records for this zone are defined at nctc.com.
NS records for this zone are defined at nctc.com.
Question and response
Question
dig mx1.nctc.com. NS
Answer
The response has no answer records.
Authority
nctc.com. 600 SOA ns1.blue.net. adminblue.blue.net. 520826382 1200 180 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0