_spf3.mail.go.th has no MX records.
Question and response
Question
dig _spf3.mail.go.th. MX
Answer
The response has no answer records.
Authority
mail.go.th. 1800 SOA amber.ns.cloudflare.com. dns.cloudflare.com. 2397930325 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0