mx1.cusae.com has no CNAME records.
Question and response
Question
dig mx1.cusae.com. NS
Answer
The response has no answer records.
Authority
cusae.com. 4998 SOA ns0.cusae.com. hostmaster.cusae.com. 2026022601 43200 7200 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0