mail.grnettelecom.com.br has no NS records.
NS records for this zone are defined at grnettelecom.com.br.
NS records for this zone are defined at grnettelecom.com.br.
Question and response
Question
dig mail.grnettelecom.com.br. NS
Answer
The response has no answer records.
Authority
grnettelecom.com.br. 1800 SOA lia.ns.cloudflare.com. dns.cloudflare.com. 2398895487 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0