mx.getcourse.ru has no NS records.
NS records for this zone are defined at getcourse.ru.
NS records for this zone are defined at getcourse.ru.
Question and response
Question
dig mx.getcourse.ru. NS
Answer
The response has no answer records.
Authority
getcourse.ru. 600 SOA ns3-l2.nic.ru. dns.nic.ru. 2020030592 1440 3600 2592000 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0