dev-back.gnm.net has no MX records.
Question and response
Question
dig dev.gnm.net. MX
Answer
The response has no answer records.
Authority
gnm.net. 60 SOA ns.gblnet.net. vvv.gnm.net. 2026022709 60 1200 1209600 259200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0