Apex domains cannot have CNAME records.
Question and response
Question
dig w4ymail.at. NS
Answer
w4ymail.at. 5 NS ns-ionos.ui-dns.de.
w4ymail.at. 5 NS ns-ionos.ui-dns.org.
w4ymail.at. 5 NS ns-ionos.ui-dns.com.
w4ymail.at. 5 NS ns-ionos.ui-dns.biz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0