mx.COMSTAR.RU has no CNAME records.
Question and response
Question
dig mx.COMSTAR.RU. NS
Answer
The response has no answer records.
Authority
comstar.ru. 5442 SOA dns0.mtu.ru. dns.mts.ru. 2025021302 3600 900 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0