Installing Dovecot is nice and easy, however, one thing that always used to confuse me is how to get subfolders when using IMAP. My old system supported it, so why doesn’t dovecot.
Turns out, it is very simple:
When you create a new folder, put a forward slash “/” on the end of the name.
So when you create your new folder, put in “Contacts/” for the name (without the quotes of course) and you’re all set. You can create subfolders underneath it.
You cannot, however, rename the Inbox to Inbox/ as Dovecot will not have a default folder to drop messages into. The new folder can only hold other folders, not messages.