mx2.ctihk.com has no CNAME records.
Question and response
Question
dig mx2.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