mail.ROUTER-OPEN.ru has no CNAME records.
Question and response
Question
dig mail.ROUTER-OPEN.ru. NS
Answer
The response has no answer records.
Authority
ROUTER-OPEN.ru. 300 SOA dns.vps1.net. admin.ROUTER-OPEN.ru. 2025111003 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0