mailstore.uspnet.usp.br has no NS records.
NS records for this zone are defined at uspnet.usp.br.
NS records for this zone are defined at uspnet.usp.br.
Question and response
Question
dig mailstore.uspnet.usp.br. NS
Answer
The response has no answer records.
Authority
uspnet.usp.br. 300 SOA a.dns.usp.br. hostmaster.usp.br. 2017065632 10800 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0