s1._domainkey.fbnet.com.br has no MX records.
Question and response
Question
dig s1.domainkey.u22591655.wl156.sendgrid.net. MX
Answer
The response has no answer records.
Authority
wl156.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2398326627 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0