mx01.ambisys.net has no CNAME records.
Question and response
Question
dig mx01.ambisys.net. NS
Answer
The response has no answer records.
Authority
ambisys.net. 809 SOA ns0.ambisys.jp. hostmaster.ambisys.com. 2025041401 10800 1800 3600000 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0