mx.noris.de has no CNAME records.
Question and response
Question
dig mx.noris.de. NS
Answer
The response has no answer records.
Authority
noris.de. 418 SOA dns0.noris.net. hostmaster.noris.net.noris.de. 2009224061 86400 86400 2419200 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0