hdcdns01.nunsys.net has no MX records.
Question and response
Question
dig hdcdns01.nunsys.net. MX
Answer
The response has no answer records.
Authority
hdcdns01.nunsys.net. 3600 SOA ns1.nunsys.net. root.hdcdns01.nunsys.net. 2025031400 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0