Hnery

It’s open source after all. Be the change you want to see in the world, I guess?

Might not tick all boxes, but etherpad may be a nice alternative for you. It’s more like a collaborative note taking thing, but gets the job done if you’re not too concerned about encryption and hide the server behind a simple HTTP authentication.

It’s a german company. Be glad you are offered e-mails at all. The official german communication medium to this day is FAX.