Apex domains cannot have CNAME records.
Question and response
Question
dig spf.proserver1.at. NS
Answer
spf.proserver1.at. 5 NS dns1.proserver1.at.
spf.proserver1.at. 5 NS dns3.proserver1.at.
spf.proserver1.at. 5 NS dns2.proserver1.at.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0