Apex domains cannot have CNAME records.
Question and response
Question
dig emsrv7.de. NS
Answer
emsrv7.de. 5 NS ns82.domaincontrol.com.
emsrv7.de. 5 NS ns81.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0