Apex domains cannot have CNAME records.
Question and response
Question
dig securemail-asp.com. NS
Answer
securemail-asp.com. 5 NS ns01.ktk-sol.co.jp.
securemail-asp.com. 5 NS ns02.ktk-sol.co.jp.
Authority
The response has no authority records.
Additional
ns01.ktk-sol.co.jp. 5 A 133.149.219.22
ns02.ktk-sol.co.jp. 5 A 158.179.185.108
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0