second-dns.netcup.net has no CNAME records.
Question and response
Question
dig second-dns.netcup.net. NS
Answer
The response has no answer records.
Authority
netcup.net. 5865 SOA acns01.xaas.systems. mail.netcup.de. 3580 14400 1800 604800 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0