spf.cyso.nl has no MX records.
Question and response
Question
dig spf.cyso.nl. MX
Answer
The response has no answer records.
Authority
cyso.nl. 300 SOA ns1.cyso.nl. dnsadmin.cysonet.com. 1771459200 16384 2048 1209600 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0