mx.mikrocenter.com.br has no CNAME records.
Question and response
Question
dig mx.mikrocenter.com.br. NS
Answer
The response has no answer records.
Authority
mikrocenter.com.br. 61749 SOA ns1.rr64.com.br. suporte.rr64.net. 2025030701 3600 1800 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0