mail.brasiltelecom.net.br has no NS records.
NS records for this zone are defined at brasiltelecom.net.br.
NS records for this zone are defined at brasiltelecom.net.br.
Question and response
Question
dig mail.brasiltelecom.net.br. NS
Answer
The response has no answer records.
Authority
brasiltelecom.net.br. 600 SOA ns02-bsa.brasiltelecom.net.br. dns.brasiltelecom.net.br. 73370 10800 3600 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0