Here is what I did:
I have created a Maildir directory in /etc/skel that looks like this:
This directory will automatically in the home directory of new users when you create a new user, along with any other files/directories in /etc/skel. You can also create "special" folders, like .Trash, and .Drafts. These are usually created by your mail client when you first define an account. Other folders that I have created, like .sent-mail and .spam. Since they have a "." in the begning, they are hidden in the Maildir, but when you launch your mail client, they will show up as normal folders. Your ~/Maildir shows up in your client as the Inbox, that's why it has it's own set of cur, new, and tmp directories. If we add a new directory in here, and name it ".test" (note the .), and give it cur, new, and tmp subdirectories, it will show up as "test" folder in your client.
Hope it helps.
Please share your configurations on how you have successfully setup Courier-IMAP, maildrop, etc.