oci.bigmachines.com has no MX records.
Question and response
Question
dig oci.bigmachines.com. MX
Answer
The response has no answer records.
Authority
oci.bigmachines.com. 300 SOA ns1.p201.dns.oraclecloud.net. hostmaster.oci.bigmachines.com. 2020121606 3600 600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0