We are using a cloud helpdesk provider that requires us to use flatforward to relay emails from outside clients (people using yahoo, aol, comcast, gmail), to an internal GW resource (servicedesk@ourgwdomain.com) out to the saas email (big_ugly_uid_account_name_@SAASservicedesk.com ) to open a service ticket.

This SAAS company is using google to host their mail.

This used to work great for a few months until recently the SAAS host (gmail) started enforcing DMARC. Now, anyone emailing from big DMARC proponents (aol, yahoo, comcast, gmail) get NDR'd when the flatfoward relays to the SAAS company.

The SAAS company is no help. they are pointing fingers at GroupWise.
My understanding is, since GroupWise is flat-forwarding it appears to the Saas host that the original message is coming from a non yahoo/aol/comcast/gmail and gets dumped. I would expect this behavior, since we are non-authorized mail servers for those domains.

Any thoughts/suggestions?