mx.customizedurl.com has no CNAME records.
Question and response
Question
dig mx.customizedurl.com. NS
Answer
The response has no answer records.
Authority
customizedurl.com. 3493 SOA ns1.sarbacane-dns.com. abuse.sarbacane.com. 2026022302 21600 3600 86400 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0