mail.dbnoc.net has no CNAME records.
Question and response
Question
dig mail.dbnoc.net. NS
Answer
The response has no answer records.
Authority
dbnoc.net. 2898 SOA dns1.hrnoc.net. hostmaster.hrnoc.net. 2026012701 28800 7200 2419200 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0