mail21.bitfibra.com.br has no MX records.
Question and response
Question
dig mail21.bitfibra.com.br. MX
Answer
The response has no answer records.
Authority
bitfibra.com.br. 86400 SOA ns1.mestrehost.com.br. noc.bitfibra.com.br. 2026020800 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0