I too have seen such broken setups. In some occasion I have sent a hint to the intermediate (probably proofpoint, not sure right now) to get their client to fix their setup. Not sure if it was followed up or even welcome.
The fact is, their email system is broken. And they are probably losing lots of legit emails. Strictly speaking, you delivered the email to them when handing it to proofpoint. It's their own fault that they choose to lose it. I would recommend to contact the target by phone if possible, since their email doesn't work [reliably]. It would interesting, from a legal point of view, who would be considered at fault (e.g. consider they dropped a DMCA notification, and they then get sued). I strongly suspect that would be the client. This is like having the Postal Service deliver certified mail to the gate of a residential area, where it is picked up by a clerk which then delivers to the individual houses... where it is discarded due to not being delivered to them by USPS. On a more practical way, since they didn't configure their intermediate IPs as trusted, they are unlikely to have setup rules restricting access to only those MTA (as they should have done). Thus, delivering email for that domain directly to Google Workspace MX, completely bypassing their mail gateway, is likely to succeed. Regards _______________________________________________ mailop mailing list [email protected] https://list.mailop.org/listinfo/mailop
