mail.gabia.co.kr has no MX records.
Question and response
Question
dig mail.gabia.co.kr. MX
Answer
The response has no answer records.
Authority
gabia.co.kr. 3600 SOA ns.gabia.co.kr. hosting.gabia.com. 2020073114 1800 600 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0