mon.inetu.net has no MX records.
Question and response
Question
dig mon.inetu.net. MX
Answer
The response has no answer records.
Authority
mon.inetu.net. 3600 SOA ns3.inetu.net. root.ns3.inetu.net. 2018042700 3600 300 86400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0