mx1.email.ncloud.com has no CNAME records.
Question and response
Question
dig mx1.email.ncloud.com. NS
Answer
The response has no answer records.
Authority
ncloud.com. 283 SOA ns1.naverncp.com. ns2.naverncp.com. 854 21600 1800 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0