mx-1.b4ne.de has no CNAME records.
Question and response
Question
dig mx-1.b4ne.de. NS
Answer
The response has no answer records.
Authority
b4ne.de. 3028 SOA dns.fucloud.de. hostmaster.b4ne.de. 2026022801 10800 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0