Apex domains cannot have CNAME records.
Question and response
Question
dig mail.a24.fi. NS
Answer
mail.a24.fi. 5 NS ns2.sedoparking.com.
mail.a24.fi. 5 NS ns1.sedoparking.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0