ns-mail01.getcourse.ru has no MX records.
Question and response
Question
dig ns-mail01.getcourse.ru. MX
Answer
The response has no answer records.
Authority
getcourse.ru. 600 SOA ns3-l2.nic.ru. dns.nic.ru. 2020030593 1440 3600 2592000 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0