smail.fubonsecurity.com.tw has no CNAME records.
Question and response
Question
dig smail.fubonsecurity.com.tw. NS
Answer
The response has no answer records.
Authority
fubonsecurity.com.tw. 6946 SOA dns1.tfn.net.tw. hostmaster.dns1.tfn.net.tw. 2024071601 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0