mail2.kcasonsa.co.kr has no MX records.
Question and response
Question
dig mail2.kcasonsa.co.kr. MX
Answer
The response has no answer records.
Authority
kcasonsa.co.kr. 300 SOA kcasonsa.co.kr. root\@.kcasonsa.co.kr. 2025122302 3600 900 1209600 10800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0