mxb.1app.com.br has no MX records.
Question and response
Question
dig mxb.1app.com.br. MX
Answer
The response has no answer records.
Authority
1app.com.br. 1800 SOA ns1.digitalocean.com. hostmaster.1app.com.br. 1772030510 10800 3600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0