mx.cloudz.jp has no CNAME records.
Question and response
Question
dig mx.cloudz.jp. NS
Answer
The response has no answer records.
Authority
cloudz.jp. 782 SOA ns000.d-53.net. dns-managers.iij.ad.jp. 1036 3600 600 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0