mx.dialhost.com.br has no CNAME records.
Question and response
Question
dig mx.dialhost.com.br. NS
Answer
The response has no answer records.
Authority
dialhost.com.br. 3145 SOA ns1.dialhost.com.br. alerta.dialhost.com.br. 2026022101 3600 600 2219200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0