Apex domains cannot have CNAME records.
Question and response
Question
dig newsletterservice.at. NS
Answer
newsletterservice.at. 4 NS dns1gr.world-direct.at.
newsletterservice.at. 4 NS dns1rz.world-direct.at.
newsletterservice.at. 4 NS dns1office.world-direct.at.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0