_spf.hiworks.co.kr has no MX records.
Question and response
Question
dig _spf.hiworks.co.kr. MX
Answer
The response has no answer records.
Authority
hiworks.co.kr. 6000 SOA ns.gabia.co.kr. hosting.gabia.com. 2021051116 1800 600 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0