mx.email.com.br has no CNAME records.
Question and response
Question
dig mx.email.com.br. NS
Answer
The response has no answer records.
Authority
email.com.br. 60 SOA ns1.penso.com.br. hostmaster.penso.com.br.email.com.br. 2026021301 7200 3600 1209600 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0