ns2.deltafibra.com.br has no MX records.
Question and response
Question
dig ns2.deltafibra.com.br. MX
Answer
The response has no answer records.
Authority
deltafibra.com.br. 3600 SOA ns1.deltafibra.com.br. hostmaster.deltafibra.com.br. 2018072300 7200 540 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0