mail01.response.oracle-mail.com has no MX records.
Question and response
Question
dig mail01.response.oracle-mail.com. MX
Answer
The response has no answer records.
Authority
oracle-mail.com. 900 SOA ns1.p201.dns.oraclecloud.net. hostmaster.oracle.com. 2025111101 21600 3600 604800 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0