Apex domains cannot have CNAME records.
Question and response
Question
dig xmailer.com.br. NS
Answer
xmailer.com.br. 5 NS ns-289.awsdns-36.com.
xmailer.com.br. 5 NS ns-550.awsdns-04.net.
xmailer.com.br. 5 NS ns-1294.awsdns-33.org.
xmailer.com.br. 5 NS ns-1578.awsdns-05.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0