mx.mostelekom.net has no CNAME records.
Question and response
Question
dig mx.mostelekom.net. NS
Answer
The response has no answer records.
Authority
mostelekom.net. 10800 SOA ns1.ncnet.ru. noc.ncnet.ru. 2019081901 10800 900 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0