https://www.open-xchange.com/ does email, office, and solves many enterprise management problems already. It can be cloud hosted or deployed online and is mostly open source (https://gitlab.open-xchange.com/frontend, pretty sure they've got everything but the "pro" stuff licensed under GPL). It's based on OpenStack, though, so hobby deployments may pose a challenge.

It's the most complete European office product I've seen so far.