mail.haeahn.com has no CNAME records.
Question and response
Question
dig mail.haeahn.com. NS
Answer
The response has no answer records.
Authority
haeahn.com. 5584 SOA ns.gabia.co.kr. hosting.gabia.com. 2023101710 1800 600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0