mx.spamservice.nl has no CNAME records.
Question and response
Question
dig mx.spamservice.nl. NS
Answer
The response has no answer records.
Authority
spamservice.nl. 3600 SOA nsplus5.2is.nl. domain-admin.2is.nl. 2026030501 14400 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0