Apex domains cannot have CNAME records.
Question and response
Question
dig raiffeisen.email. NS
Answer
raiffeisen.email. 5 NS ns68.domaincontrol.com.
raiffeisen.email. 5 NS ns67.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0