Apex domains cannot have CNAME records.
Question and response
Question
dig mail.quantum.ru. NS
Answer
mail.quantum.ru. 5 NS ns1.quantum.ru.
mail.quantum.ru. 5 NS ns.quantum.ru.
Authority
The response has no authority records.
Additional
ns.quantum.ru. 1 A 213.170.64.33
ns1.quantum.ru. 1 A 213.170.65.33
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0