fxx.domainkey.u50588907.wl158.sendgrid.net has no NS records.
NS records for this zone are defined at wl158.sendgrid.net.
NS records for this zone are defined at wl158.sendgrid.net.
Question and response
Question
dig fxx.domainkey.u50588907.wl158.sendgrid.net. NS
Answer
The response has no answer records.
Authority
wl158.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2399833529 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0