mx20.ctimail.com has no CNAME records.
Question and response
Question
dig mx20.ctimail.com. NS
Answer
The response has no answer records.
Authority
ctimail.com. 3457 SOA ns1.hkbn.net. sysadm.ns1.hkbn.net. 2026012801 3600 1800 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0