mx.secureweb.jp has no CNAME records.
Question and response
Question
dig mx.secureweb.jp. NS
Answer
The response has no answer records.
Authority
secureweb.jp. 895 SOA ns-e.secureweb.jp. dns-managers.iij.ad.jp. 124 3600 1800 3600000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0