mx1.ctihk.com has no NS records.
NS records for this zone are defined at ctihk.com.
NS records for this zone are defined at ctihk.com.
Question and response
Question
dig mx1.ctihk.com. NS
Answer
The response has no answer records.
Authority
ctihk.com. 3600 SOA ns1o.ctihk.com. sysadm.ns1o.ctihk.com. 2026012801 3600 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0