mx.doctorout.com has no NS records.
NS records for this zone are defined at doctorout.com.
NS records for this zone are defined at doctorout.com.
Question and response
Question
dig mx.doctorout.com. NS
Answer
The response has no answer records.
Authority
doctorout.com. 3600 SOA dns.doctorout.com. hostmaster.doctorout.com. 1685221454 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0