mx.unitymedia.de has no CNAME records.
Question and response
Question
dig mx.unitymedia.de. NS
Answer
The response has no answer records.
Authority
unitymedia.de. 7058 SOA ns1.vodafone-ip.de. hostmaster.adm.arcor.net. 2026022400 28800 14400 1814400 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0