wl181.sendgrid.net has no MX records.
Question and response
Question
dig wl181.sendgrid.net. MX
Answer
The response has no answer records.
Authority
wl181.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2397398159 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0