mailling.blueweb.co.kr has no CNAME records.
Question and response
Question
dig mailling.blueweb.co.kr. NS
Answer
The response has no answer records.
Authority
blueweb.co.kr. 600 SOA ns1.blueweb.co.kr. system.blueweb.co.kr. 2026020402 10800 3600 432000 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0