s2._domainkey.axcient.com has no MX records.
Question and response
Question
dig s2.domainkey.u23552801.wl052.sendgrid.net. MX
Answer
The response has no answer records.
Authority
wl052.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2397567857 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0