spf.onesignal.email has no MX records.
Question and response
Question
dig spf.onesignal.email. MX
Answer
The response has no answer records.
Authority
onesignal.email. 1800 SOA ashton.ns.cloudflare.com. dns.cloudflare.com. 2397601692 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0