spf1.denit.nl has no MX records.
Question and response
Question
dig spf1.denit.nl. MX
Answer
The response has no answer records.
Authority
denit.nl. 600 SOA ns1.masterdns.nl. hostmaster.denit.net. 2026012300 14400 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0