webmail.hosting.co.kr has no CNAME records.
Question and response
Question
dig webmail.hosting.co.kr. NS
Answer
The response has no answer records.
Authority
hosting.co.kr. 5435 SOA ns1.hosting.co.kr. admin.hosting.co.kr. 207 21600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0