mx.gblnet.net has no CNAME records.
Question and response
Question
dig mx.gblnet.net. NS
Answer
The response has no answer records.
Authority
gblnet.net. 4529 SOA ns.gblnet.net. vvv.gblnet.net. 2026021602 10800 1200 1209600 259200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0