mx.ROSTELECOM-CC.RU has no CNAME records.
Question and response
Question
dig mx.ROSTELECOM-CC.RU. NS
Answer
The response has no answer records.
Authority
rostelecom-cc.ru. 3189 SOA ns.rostelecom-cc.ru. dns.rostelecom-cc.ru. 2829247455 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0