_spf.heysender.com has no MX records.
Question and response
Question
dig _spf.heysender.com. MX
Answer
The response has no answer records.
Authority
heysender.com. 300 SOA ns1.curanet.dk. hostmaster.curanet.dk. 2025111401 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0