u15201723.wl224.sendgrid.net has no NS records.
NS records for this zone are defined at wl224.sendgrid.net.
NS records for this zone are defined at wl224.sendgrid.net.
Question and response
Question
dig u15201723.wl224.sendgrid.net. NS
Answer
The response has no answer records.
Authority
wl224.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2399224933 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0