_mx.inter-it.nl has no CNAME records.
Question and response
Question
dig _mx.inter-it.nl. NS
Answer
The response has no answer records.
Authority
inter-it.nl. 3436 SOA ns.inter-it.nl. dns-admin.inter-it.nl. 2026012201 10800 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0