Apex domains cannot have CNAME records.
Question and response
Question
dig mx1.KUBTEL.RU. NS
Answer
mx1.kubtel.ru. 5 NS ns4.kubtel.ru.
mx1.kubtel.ru. 5 NS ns3.kubtel.ru.
Authority
The response has no authority records.
Additional
ns4.KUBTEL.RU. 5 A 46.18.200.201
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0