mx.sendgrid.net has no TXT records.
Question and response
Question
dig mx.sendgrid.net. TXT
Answer
The response has no answer records.
Authority
sendgrid.net. 180 SOA ns10.dnsmadeeasy.com. dns.dnsmadeeasy.com. 2011293935 14400 600 1728000 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0