auth01.dns.trueserver.nl has no CNAME records.
Question and response
Question
dig auth01.dns.trueserver.nl. NS
Answer
The response has no answer records.
Authority
trueserver.nl. 2161 SOA auth01.dns.trueserver.nl. hostmaster.trueserver.nl. 2017060616 86400 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0