_spf.onlinespamfilter.nl has no MX records.
Question and response
Question
dig _spf.onlinespamfilter.nl. MX
Answer
The response has no answer records.
Authority
onlinespamfilter.nl. 600 SOA ns1.argewebhosting.eu. hostmaster.argeweb.nl. 2025073100 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0