relay4.ksc.net.th has no MX records.
Question and response
Question
dig relay4.ksc.net.th. MX
Answer
The response has no answer records.
Authority
ksc.net.th. 86400 SOA ns.ksc.co.th. hostmaster.ns.ksc.co.th. 2025111800 3600 7200 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0