gpphosted.com has no MX records.
Question and response
Question
dig gpphosted.com. MX
Answer
The response has no answer records.
Authority
gpphosted.com. 900 SOA ns1.proofpoint.com. ops.proofpoint.com. 188547 1800 180 2419200 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0