Apex domains cannot have CNAME records.
Question and response
Question
dig wl150.sendgrid.net. NS
Answer
wl150.sendgrid.net. 2 NS aisha.ns.cloudflare.com.
wl150.sendgrid.net. 2 NS devin.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0