Very interestingly, most comments seem to focus on trying to propose you a "magic" product. The problem you are trying to solve is not a technology but a human

Very interestingly, most comments seem to focus on trying to propose you a "magic" product. The problem you are trying to solve is not a technology but a human issue: most organizations don't have the resources anymore to handle the technical complexity required to operate an integrated collaboration platform that is fully interoperable both within the organization and outside. The shortest answer is that Microsoft solved this problem by hiring lots of people and making it possible (Google, too, but that keeps you with the same compliance issue). The first problem EU States need to solve is human resources. Then they will be able to discuss possible solutions. Starting the discussion on how to replace Microsoft by looking for products is basically running into a 100% failure trajectory. My 2 cents.