webmail.tw1.com has no CNAME records.
Question and response
Question
dig webmail.tw1.com. NS
Answer
The response has no answer records.
Authority
tw1.com. 4337 SOA ns1.tw1.com. root.ns1.tw1.com. 2025050521 3600 900 1209600 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0