dns4.midco.net has no MX records.
Question and response
Question
dig dns4.midco.net. MX
Answer
The response has no answer records.
Authority
midco.net. 900 SOA dns3.midco.net. hostmaster.midco.net. 2018117011 10800 3600 2419200 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0