Apex domains cannot have CNAME records.
Question and response
Question
dig prd.postifi.posticloud.fi. NS
Answer
prd.postifi.posticloud.fi. 5 NS ns-803.awsdns-36.net.
prd.postifi.posticloud.fi. 5 NS ns-1439.awsdns-51.org.
prd.postifi.posticloud.fi. 5 NS ns-1609.awsdns-09.co.uk.
prd.postifi.posticloud.fi. 5 NS ns-430.awsdns-53.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0