ns.mail2000.com.tw has no CNAME records.
Question and response
Question
dig ns.mail2000.com.tw. NS
Answer
The response has no answer records.
Authority
mail2000.com.tw. 2694 SOA ns-183.awsdns-22.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0