Apex domains cannot have CNAME records.
Question and response
Question
dig dtmail2.com.br. NS
Answer
dtmail2.com.br. 5 NS ns-178.awsdns-22.com.
dtmail2.com.br. 5 NS ns-575.awsdns-07.net.
dtmail2.com.br. 5 NS ns-1468.awsdns-55.org.
dtmail2.com.br. 5 NS ns-1891.awsdns-44.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0