mxt.f1.k8.com.br has no MX records.
Question and response
Question
dig mxt.f1.k8.com.br. MX
Answer
The response has no answer records.
Authority
f1.k8.com.br. 3600 SOA nsa1.k8.com.br. dnsmasters.k8.com.br. 1845 3600 300 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0