mail.corenap.com has no MX records.
Question and response
Question
dig mail.corenap.com. MX
Answer
The response has no answer records.
Authority
mail.corenap.com. 3600 SOA ns1.dfw.databank.com. ipadmin.databank.com. 2024022803 7200 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0