IMAP->IMAP: can't create target folder, already exists

[Chris Shenton <chris@xxxxxxxxxxx>]

I'm being forced to move from a courier-imap server to Exchange (don't
ask) and am trying to use offlineimap to migrate my stored mail.  It
seems to work fine, except when it tries to create a folder on the
destination server which already exists:

  RuntimeError: Repository HEMI could not create folder Inbox/Sent:
  ('NO', ['An object by the same name was found.'])

The Exchange server came pre-populated with a few folders.  In this
case, the "Sent" folder was created by a previous run of offlineimap,
but it died due to a Python Tk problem I'm having on the OS X I'm
running it on.  When I start offlineimap again, it finds the folder it
already created and fails. 

Is there a way I  can get offlineimap to ignore the fact that the
folder already exists and just use it, rather than failing because it
couldn't create it?

I found one query similar to this in the list archives but didn't see
any answer. 

Thanks.