wl156.sendgrid.net has no MX records.
Question and response
Question
dig wl156.sendgrid.net. MX
Answer
The response has no answer records.
Authority
wl156.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2397379038 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0