Apex domains cannot have CNAME records.
Question and response
Question
dig mail24server.com. NS
Answer
mail24server.com. 5 NS ns4fpy.name.com.
mail24server.com. 5 NS ns3fgq.name.com.
mail24server.com. 5 NS ns1cwy.name.com.
mail24server.com. 5 NS ns2glx.name.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0