Hello,
as we all know from the big webmail-services like hotmail.com, yahoo.com, web.de and so on, several folders exist and nobody can remove them for a good reason, because some services rely on them: Trash, Junk, Sent. Can can't remove Trash, because every deleted message is just moved here. You can't remove Junk, because all messages recognized as spam is moved here. And you can't remove Sent, because all messages you sent through the webmail are saved here. With the common courier-imap, everyone either has to bloat his webmail client with permanent checking if the required folders exist and recreate them if needed, or he has to patch courier-imap each time a new release appears to extend to this certain functionality. So why not just include this feature in courier-imap generally? I think there's no need to handle these folders on a per mailbox basis. Courier-imap could look at a file that contains the unremovable folders (one per line) and deny deletion of this folders. Now you might say: "You could prevent deletion of this folders in your webmail client as well." But that's only the half of the truth, because if you just want to see webmail as one option of accessing the emails, but POP3 and IMAP access is offered as well, then deletion must be restricted at IMAP side. I didn't implement this feature yet, but I'll need it in near future, so either someone else implements it our I would send you a patch after I implemented it.
Regards Marten Lehmann