spfext.spf.ksc.net has no MX records.
Question and response
Question
dig spfext.spf.ksc.net. MX
Answer
The response has no answer records.
Authority
spf.ksc.net. 3600 SOA ns2.ksc.net. hostmaster.ns.ksc.co.th. 2019122417 3600 900 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0