wl100.sendgrid.net has no MX records.
Question and response
Question
dig wl100.sendgrid.net. MX
Answer
The response has no answer records.
Authority
wl100.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2398389115 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0