mx.mailgrid.net.br has no CNAME records.
Question and response
Question
dig mx.mailgrid.net.br. NS
Answer
The response has no answer records.
Authority
mailgrid.net.br. 898 SOA ns-1289.awsdns-33.org. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0