mail.schwitzing.de has no CNAME records.
Question and response
Question
dig mail.schwitzing.de. NS
Answer
The response has no answer records.
Authority
schwitzing.de. 10 SOA ns2.knipp.de. hostmaster.schwitzing.de. 2026012702 3600 1800 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0