mail.ZCDN.RU has no CNAME records.
Question and response
Question
dig mail.ZCDN.RU. NS
Answer
The response has no answer records.
Authority
zcdn.ru. 1014 SOA ns2.zcdn.ru. adm.zcdn.ru. 2025092618 14400 7200 2419200 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0