I have an Ubuntu 16.04 server with ISPConfig 3.1 and many websites installed. I had to move some websites from an old server to a new one. I created the same mailboxes, but I need to retrieve the emails from the old server. I tried with Roundcube but it only allows to export emails one by one. I'm thinking about using the backup files from ISPConfig in order to move them to the new server and restore them. Is it possible to do this? Is there another way to retrieve the emails?