mail.ktcloud.com has no CNAME records.
Question and response
Question
dig mail.ktcloud.com. NS
Answer
The response has no answer records.
Authority
ktcloud.com. 5260 SOA ns.kornet.net. domain.ns.kornet.net. 2026021301 43200 3600 604800 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0