mx2ed5.netcup.net has no CNAME records.
Question and response
Question
dig mx2ed5.netcup.net. NS
Answer
The response has no answer records.
Authority
netcup.net. 6650 SOA acns01.xaas.systems. mail.netcup.de. 3578 14400 1800 604800 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0