spf.mailtastic.com has no MX records.
Question and response
Question
dig spf.mailtastic.com. MX
Answer
The response has no answer records.
Authority
mailtastic.com. 600 SOA ns77.domaincontrol.com. dns.jomax.net. 2025112400 28800 7200 604800 600
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0