Apex domains cannot have CNAME records.
Question and response
Question
dig protection.outlook.de. NS
Answer
protection.outlook.de. 5 NS ns3-36.azure-dns.org.
protection.outlook.de. 5 NS ns1-36.azure-dns.com.
protection.outlook.de. 5 NS ns2-36.azure-dns.net.
protection.outlook.de. 5 NS ns4-36.azure-dns.info.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0