Apex domains cannot have CNAME records.
Question and response
Question
dig message-flow.net. NS
Answer
message-flow.net. 4 NS charles.ns.cloudflare.com.
message-flow.net. 4 NS athena.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0