f.dns.kr has no MX records.
Question and response
Question
dig f.dns.kr. MX
Answer
The response has no answer records.
Authority
dns.kr. 86400 SOA g.dns.kr. domain-manager.nic.or.kr. 1904030500 3600 900 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0