I made a small modification to create folders at IMAP account and mark the e-mails as Seen:

diff imap_upload.py imap_upload.py-original
300,301c300
< self.imap.create(self.box)
< return self.imap.append(self.box, '\Seen', delivery_time, message)
---
> return self.imap.append(self.box, [], delivery_time, message)

It's an incomplete hack because it assumes that folder doesn't exist at IMAP account.

Regards,

Josep Pujadas-Jubany