mail.rightside.ru has no CNAME records.
Question and response
Question
dig mail.rightside.ru. NS
Answer
The response has no answer records.
Authority
rightside.ru. 76 SOA ns.rightside.ru. root.rightside.ru. 2026022401 10800 3600 604800 1400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0