Update: We are still working to receive further information from Proofpoint and get the issue resolved ASAP. In the meantime, a valid workaround is to switch your EveryCloud smarthost to the following:
Once changed, new outbound email that is sent, will be delivered okay. The EveryCloud SPF record of "v=spf1 include:spf.everycloudtech.com -all" includes this server cluster.
Posted 7 months ago. Oct 26, 2017 - 18:06 BST
Outbound emails going to 3rd parties using Proofpoint are being deferred by Proofpoint.
We have raised the issue with Proofpoint and are awaing there response.