mx.drilldocter.com has no NS records.
NS records for this zone are defined at drilldocter.com.
NS records for this zone are defined at drilldocter.com.
Question and response
Question
dig mx.drilldocter.com. NS
Answer
The response has no answer records.
Authority
drilldocter.com. 3600 SOA dns.drilldocter.com. hostmaster.drilldocter.com. 1533881471 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0