u21890913.wl164.sendgrid.net has no NS records.
NS records for this zone are defined at wl164.sendgrid.net.
NS records for this zone are defined at wl164.sendgrid.net.
Question and response
Question
dig u21890913.wl164.sendgrid.net. NS
Answer
The response has no answer records.
Authority
wl164.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2399130998 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0