mx.premium-a.ru has no CNAME records.
Question and response
Question
dig mx.premium-a.ru. NS
Answer
The response has no answer records.
Authority
premium-a.ru. 440 SOA vip154.hosting.reg.ru. support.reg.ru. 2022091567 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0