mtest.onhgcloud.com has no MX records.
Question and response
Question
dig mtest.onhgcloud.com. MX
Answer
The response has no answer records.
Authority
onhgcloud.com. 300 SOA ns1.p201.dns.oraclecloud.net. hostmaster.onhgcloud.com. 13 3600 600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0