"Path to IMAP root folder" is a badly named setting that has caused a lot of confusion recently. To be able to explain this setting, I need to give a bit of background about the way IMAP works. IMAP has a concept called namespaces (defined in RFC 2342) which allows grouping of mailboxes. Each user has a personal namespace. Sometimes, users also have access to a Shared or Other Users' namespace. Be default, Opera 8.0 Preview 5 will only list mailboxes within the user's personal namespace or the Shared namespace.
Now, here's where the setting comes into play. If you enter something in the "Path to IMAP root folder" setting, Opera will list mailboxes in that namespace in addition to the user's personal namespace and the Shared namespace.
Since Opera restricts the namespaces available to the user, we've come to the conclusion that we need to allow the user better control over the namespaces Opera lists and the way they're presented to the user. These changes will probably not be in 8.0 (should the new IMAP back-end go in), but hopefully not too long afterward.
EDIT: And it turns out this setting was broken. ;) It should be fixed now for the next release.
