We are almost ready!
The development has lasted more than expected because we want to implement the relationships from emails to labels (how Gmail intends them). In the document of the Gmail IMAP Extensions, about “Access to Gmail labels“, we can read:
Gmail treats labels as folders for the purposes of IMAP. As such, labels can be modified using the standard IMAP commands that act on folders.
Gmail provides a unique message ID for each email so that a unique message may be identified across multiple folders. For our backup will be the same!
We have created a DB to store relationships while the emails will be stored each one in a single file.