mxt.f1.k8.com.br has no CNAME records.
Question and response
Question
dig mxt.f1.k8.com.br. NS
Answer
The response has no answer records.
Authority
f1.k8.com.br. 3172 SOA nsa1.k8.com.br. dnsmasters.k8.com.br. 1847 3600 300 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0