mx2.KUBTEL.RU has no CNAME records.
Question and response
Question
dig mx2.KUBTEL.RU. NS
Answer
The response has no answer records.
Authority
kubtel.ru. 300 SOA ns5.kubtel.ru. noc.kubtel.ru. 2026020400 3600 900 3600000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0