@girish personally I would enjoy the option to limit the E-Mail manager to the groups they are part of. For example some clients use so little resources like only a website with E-Mail that it doesn’t make sense to give them a dedicated server but instead put a few on the same.
Very good points as well, however as @girish says, as this would require to implement shared resources the idea is easier said than done. On the other hand, I personally can't see why it would not make sense to provide dedicated VPS at low cost for its own little resources needs to such client. In when you think about it, any client can grow and in such case the client is already set to scale without any more hassle. Cloudron is not too heavy for a simple basic use as it will adjust its own resources need only for the needs of the installed apps.
Now it would be nice if they could configure their own emails without being able to see let alone change the configuration of others.
Moreover, as explained previously if you install Cloudron for the client, a 10 bucks per month VPS would be more than perfect for such low needs, as superadmin you keep full control of the instance's management for the client and you give it admin privileges so it can fully manage its mail server. And with the upcoming multiple instances of Cloudron feature that should should become easier to manage from your side as well. 😊