ns3.dnsever.co.kr has no MX records.
Question and response
Question
dig ns3.dnsever.co.kr. MX
Answer
The response has no answer records.
Authority
dnsever.co.kr. 14400 SOA ns6.dnsever.co.kr. admin.dnsever.com. 1742953231 86400 600 1209600 14400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0