mx.truezuid.nl has no CNAME records.
Question and response
Question
dig mx.truezuid.nl. NS
Answer
The response has no answer records.
Authority
truezuid.nl. 2349 SOA nsauth1.pinkzuid.nl. hostmaster.pinkzuid.nl. 2023050902 28800 7200 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0