_spf.one.th has no MX records.
Question and response
Question
dig _spf.one.th. MX
Answer
The response has no answer records.
Authority
one.th. 300 SOA ns2.inet.co.th. root.one.th. 8538 3600 600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0