@kev never considered Threema? Servers in Switzerland. Apps are fully open source and inspectable. (although new accounts can apparently not be created with the open source version of the apps or something). It is E2E and you can chose to share your addressbook (as hashes) or not.
@spaetz@kev using #Threema too but people don't want to pay the license to talk to you. Making the move to #Signal is already a challenge. Now I would consider their enterprise plan if I had to chose a messaging app for my company.