mailfilter.myrootnet.nl has no CNAME records.
Question and response
Question
dig mailfilter.myrootnet.nl. NS
Answer
The response has no answer records.
Authority
myrootnet.nl. 600 SOA nsauth.myrootnet.com. root.rootnet.nl. 2026022601 14400 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0