I've had this issue and it's been bugging me forever... I've searched and I can't seem to find an answer. I have a personal email account through fastmail.fm. On my laptop all of my folders display nicely (meaning... if I open it I'll see:
Accountant
Inbox
Saved
Spam
....
And so on.
But, on my desktop, the folders are displayed in a hierarchy. If I open the mail account I'm only shown the inbox. I then have to click on the + sign to the left of the inbox to see all the other folders. So... how can I take what my desktop is displaying now and get it to display like my laptop does?