x2.mailcloud.com.tw has no CNAME records.
Question and response
Question
dig x2.mailcloud.com.tw. NS
Answer
The response has no answer records.
Authority
mailcloud.com.tw. 889 SOA ns-848.awsdns-42.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0