mx4.hrnoc.net has no CNAME records.
Question and response
Question
dig mx4.hrnoc.net. NS
Answer
The response has no answer records.
Authority
hrnoc.net. 3188 SOA hostmaster.hrnoc.net. 2022031501. 28800 7200 2419200 7200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0