I have a customer with two O365 tenant accounts. They did not anticipate the need for the 2 organizations to work together and predictably have run into trouble sharing files in SharePoint.
Merging the 2 tenants is not a good option as there are too many users at both and it would be painful and disruptive.
I've tried to manage the external sharing options in SharePoint, but that only creates problems because it would permit sharing via a domain white-list, and allow external sharing to other outside domains only by specific addition to the white-list.
I want to allow an experience similar to how it would work if they were in the same tenant.
I'm wondering if there is a way to add a trust between tenants as in the "old days" of managing domains, and creating a trust relation between the two organizations.
I just want it to work as if users in two tenants were in one.