Not necessarily (depends on how you define e2e). One could handle group messaging in a way where membership gives you full historical access vs. only when you were subscribed. In a corp environment you might even require that some groups remain server-side so you can instantly revoke access.
Allowing different security models for different groups would make sense, as long as you could communicate the security models to users and admins somehow.
Allowing different security models for different groups would make sense, as long as you could communicate the security models to users and admins somehow.
e2e for direct user to user makes sense.