s1._domainkey.syncedtool.com has no MX records.
Question and response
Question
dig s1.domainkey.u250297.wl048.sendgrid.net. MX
Answer
The response has no answer records.
Authority
wl048.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2397421851 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0