Apex domains cannot have CNAME records.
Question and response
Question
dig esn.at. NS
Answer
esn.at. 5 NS ns1-38.azure-dns.com.
esn.at. 5 NS ns3-38.azure-dns.org.
esn.at. 5 NS ns2-38.azure-dns.net.
esn.at. 5 NS ns4-38.azure-dns.info.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0