internal.akadns.net has no MX records.
Question and response
Question
dig internal.akadns.net. MX
Answer
The response has no answer records.
Authority
akadns.net. 180 SOA internal.akadns.net. hostmaster.akamai.com. 1741200000 90000 90000 90000 180
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0