mail.hrnoc.net has no MX records.
Question and response
Question
dig mail.hrnoc.net. MX
Answer
The response has no answer records.
Authority
hrnoc.net. 3600 SOA hostmaster.hrnoc.net. 2022031501. 28800 7200 2419200 7200 3600
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0