mx2.proofpoint.com.gslb.pphosted.com has no MX records.
Question and response
Question
dig mx2.proofpoint.com.gslb.pphosted.com. MX
Answer
The response has no answer records.
Authority
proofpoint.com.gslb.pphosted.com. 60 SOA ns-sc4.proofpoint.com. ops.proofpoint.com. 166 10800 3600 604800 60
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0