This might be helpful -
https://ipcheck.proofpoint.com/ From: NANOG <nanog-boun...@nanog.org> On Behalf Of Tim Donahue Sent: Thursday, 10 January 2019 11:21 AM To: nanog@nanog.org Subject: Proofpoint Mail Delivery Issues Hi all, Sorry for the noise, but one of my clients is getting the standard "it's the other guy's fault" with some email delivery issues to/from Proofpoint "Enterprise" customers. If there is anyone from Proofpoint support monitoring this list, some assistance troubleshooting email delivery issues would be greatly appreciated. Thank you, Tim Donahue
