i.ppops.net has no MX records.
Question and response
Question
dig i.ppops.net. MX
Answer
The response has no answer records.
Authority
ppops.net. 3600 SOA ns1.proofpoint.com. ops.proofpoint.com. 2017040790 3600 1800 604800 21600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0