spf.mxthunder.com has no MX records.
Question and response
Question
dig spf.mxthunder.com. MX
Answer
The response has no answer records.
Authority
spf.mxthunder.com. 172800 SOA ns.dnsbox.net. hostmaster.dnsbox.net. 2023111410 10000 3600 604800 172800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0