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. 5350 SOA ns.GbLNet.RU. vvv.GbLNet.RU. 2026030201 10800 1200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0