I've recently started preparing a virtualised (Using Plesk/Virtuozzo) web server with Courier IMAP. I'm noticing operations involving opening folders are taking 5-10 seconds before anything seems to happen. This happens when connecting via Thunderbird or by Squirrelmail which I've installed on the server. I have access to another supposedly identical web server and these operations are near instantaneous so it would seem to be something set up differently between the two servers.