mx.mijnspamfilter.nl has no CNAME records.
Question and response
Question
dig mx.mijnspamfilter.nl. NS
Answer
The response has no answer records.
Authority
mijnspamfilter.nl. 300 SOA ns1.mijndnsserver.nl. hostmaster.mijnspamfilter.nl. 2026022503 28800 7200 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0