s1._domainkey.oi.com.br has no NS records.
NS records for this zone are defined at oi.com.br.
NS records for this zone are defined at oi.com.br.
Question and response
Question
dig s1.domainkey.u6262028.wl029.sendgrid.net. NS
Answer
The response has no answer records.
Authority
wl029.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2399883088 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0