mtz1.oracleemaildelivery.com has no MX records.
Question and response
Question
dig mtz1.oracleemaildelivery.com. MX
Answer
The response has no answer records.
Authority
mtz1.oracleemaildelivery.com. 300 SOA ns1.p68.dns.oraclecloud.net. hostmaster.mtz1.oracleemaildelivery.com. 719657 3600 600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0