ns2.certto.com.br has no MX records.
Question and response
Question
dig ns2.certto.com.br. MX
Answer
The response has no answer records.
Authority
certto.com.br. 900 SOA ns1.certto.com.br. support.certto.com.br. 2026013000 43200 3600 1209600 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0