Apex domains cannot have CNAME records.
Question and response
Question
dig meuemail.seg.br. NS
Answer
meuemail.seg.br. 5 NS carioca.ns.cloudflare.com.
meuemail.seg.br. 5 NS sri.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0