mx.casjay.app has no CNAME records.
Question and response
Question
dig mx.casjay.app. NS
Answer
The response has no answer records.
Authority
casjay.app. 5556 SOA dns.casjay.app. dns-admin.casjay.app. 2026010364 10800 3600 1209600 38400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0