Apex domains cannot have CNAME records.
Question and response
Question
dig omkcmail.ru. NS
Answer
omkcmail.ru. 5 NS ns.omkc.ru.
omkcmail.ru. 5 NS ns2.omkc.ru.
Authority
The response has no authority records.
Additional
ns.omkc.ru. 5 A 217.25.208.6
ns2.omkc.ru. 5 A 217.25.209.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0