kundenmail.dsinet.de has no CNAME records.
Question and response
Question
dig kundenmail.dsinet.de. NS
Answer
The response has no answer records.
Authority
dsinet.de. 300 SOA ns.dsinet.eu. hostmaster.dsi.net. 2026022615 28800 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0