mail.ratm.ru has no CNAME records.
Question and response
Question
dig mail.ratm.ru. NS
Answer
The response has no answer records.
Authority
ratm.ru. 771 SOA ns.ratm.ru. root.ratm.ru. 2025120909 86400 900 2419200 432000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0