spf4.csod.com has no MX records.
Question and response
Question
dig spf4.csod.com. MX
Answer
The response has no answer records.
Authority
csod.com. 300 SOA ns1-ext-prd.csod.com. hostmaster.csod.com. 670758 300 60 1209600 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0