Apex domains cannot have CNAME records.
Question and response
Question
dig enco-gera.de. NS
Answer
enco-gera.de. 5 NS nsa2.schlundtech.de.
enco-gera.de. 5 NS nsd2.schlundtech.de.
enco-gera.de. 5 NS nsc2.schlundtech.de.
enco-gera.de. 5 NS nsb2.schlundtech.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0