Apex domains cannot have CNAME records.
Question and response
Question
dig mailasp.com.tw. NS
Answer
mailasp.com.tw. 5 NS ns.mail2000.com.tw.
mailasp.com.tw. 5 NS ns2.mail2000.com.tw.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0