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