koreacentral.cloudapp.azure.com has no MX records.
Question and response
Question
dig koreacentral.cloudapp.azure.com. MX
Answer
The response has no answer records.
Authority
koreacentral.cloudapp.azure.com. 60 SOA ns1-01.azure-dns.com. msnhst.microsoft.com. 1 900 300 604800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0