www.equinix.com.edgekey.net has no MX records.
Question and response
Question
dig e13414.b.akamaiedge.net. MX
Answer
The response has no answer records.
Authority
b.akamaiedge.net. 1000 SOA n0b.akamaiedge.net. hostmaster.akamai.com. 1772247541 1000 1000 1000 1800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0