mail.kwberlin.com has no CNAME records.
Question and response
Question
dig mail.kwberlin.com. NS
Answer
The response has no answer records.
Authority
kwberlin.com. 300 SOA ns1.first-ns.de. sys\.dolores.kwberlin.com. 2026022302 3600 900 1209600 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0