mx2.vuurwerk.nl has no CNAME records.
Question and response
Question
dig mx2.vuurwerk.nl. NS
Answer
The response has no answer records.
Authority
vuurwerk.nl. 8 SOA anahi.ns.cloudflare.com. dns.cloudflare.com. 2395265218 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0