Currently Airmail seems to flatten then entire IMAP hierarchy (I've just spent (again) about an hour digging around in my Dovecot configuration to try and find the problem, before deciding it seems to be Airmail; Apple Mail handles the folders correctly).

As my folder hierarchy contains a bunch of parent folders whose child folders all have the same name, it gets very confusing in the Airmail folder view.

Handling IMAP folders properly seems like an obvious improvement at this point.