mail2.mav.com.br has no NS records.
NS records for this zone are defined at mav.com.br.
NS records for this zone are defined at mav.com.br.
Question and response
Question
dig mail2.mav.com.br. NS
Answer
The response has no answer records.
Authority
mav.com.br. 1200 SOA ns1.supramail.com.br. suporte.supramail.com.br. 2016032318 10800 3600 604800 3600
Additional
. 0 OPT ; payload 2800, xrcode 0, version 0, flags 0