mx.anet.net.tw has no CNAME records.
Question and response
Question
dig mx.anet.net.tw. NS
Answer
The response has no answer records.
Authority
anet.net.tw. 299 SOA dns1.tfn.net.tw. dns_admin.tfn.net.tw. 2025062601 10800 3600 86400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0