mX.GbLNet.RU has no CNAME records.
Question and response
Question
dig mX.GbLNet.RU. NS
Answer
The response has no answer records.
Authority
GbLNet.ru. 2317 SOA ns.GbLNet.ru. vvv.GbLNet.ru. 2026030201 10800 1200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0