_spf.dfn.nl has no MX records.
Question and response
Question
dig _spf.dfn.nl. MX
Answer
The response has no answer records.
Authority
dfn.nl. 3600 SOA ns1.dfn.nl. hostmaster.dfn.nl. 2026022320 14400 3600 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0