_dmarc.sendgrid.net has no NS records.
NS records for this zone are defined at sendgrid.net.
NS records for this zone are defined at sendgrid.net.
Question and response
Question
dig _dmarc.sendgrid.net. NS
Answer
The response has no answer records.
Authority
sendgrid.net. 180 SOA ns10.dnsmadeeasy.com. dns.dnsmadeeasy.com. 2011294159 14400 600 1728000 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0