ruh1.oracleemaildelivery.com has no MX records.
Question and response
Question
dig ruh1.oracleemaildelivery.com. MX
Answer
The response has no answer records.
Authority
ruh1.oracleemaildelivery.com. 300 SOA ns1.p68.dns.oraclecloud.net. hostmaster.ruh1.oracleemaildelivery.com. 213544 3600 600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0