server18.mailgrid.com.br has no CNAME records.
Question and response
Question
dig server18.mailgrid.com.br. NS
Answer
The response has no answer records.
Authority
mailgrid.com.br. 834 SOA ns-889.awsdns-47.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0