If I understand correctly your Italian, you are asking if there is a way to leave all messages marked unread on the server with an IMAP connection (account).
In case of IMAP, all messages on all devices and the server have exactly the same status. Think of your device being a window into what you have on the server, and when you change something on the device, you are actually making the same changes on the server (and vice-versa). So, you always have a 1:1 correspondence between the messages on the server and on the device (and all devices/e-mail programs).
So, if you want the messages to remain unread on the server, you need to disable them being marked read on the device. For that: Aquamail Settings -> Message View -> Mark messages as read -> "Never automatically".