mail.cdom.de has no CNAME records.
Question and response
Question
dig mail.cdom.de. NS
Answer
The response has no answer records.
Authority
cdom.de. 300 SOA ns1.cdom.de. hostmaster.cdom.de. 2026022564 3600 600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0