sdc.prod.communities.salesforce.cdn.edgekey.net has no MX records.
Question and response
Question
dig e78038.dsca.akamaiedge.net. MX
Answer
The response has no answer records.
Authority
dsca.akamaiedge.net. 1000 SOA n0dsca.akamaiedge.net. hostmaster.akamai.com. 1772667237 1000 1000 1000 1800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0