Yesterday a customer’s compromised outbound accounts (albeit brief) caused our SMTP AUTH server to become blacklisted at Proofpoint. Outbound mail authorization was revoked for that customer in accordance with our policies, however the Proofpoint block lingers.
If you are having trouble contacting someone behind Proofpoint you should encourage them to contact their mail host and/or Proofpoint for resolution. Although we are attempting to reach out ourselves, companies like Proofpoint are more likely to listen to their own customer’s complains about losing legitimate mail than they will listen to us.
As far as we are aware this issue is limited to Proofpoint.
UPDATE : This issue has been resolved as of August 23, 2016.