Repair headers with envelope via offlineimap

[Henning Hollermann]

Hi there,

I have a FirstClass E-Mail Server which has unfortunately a broken
IMAP-Module. With some effords at least I'm able to fetch messages from
the Server with offlineimap to migrate a couple of users to another server.

Received messages are fetched correctly, but Sent messages break because
the FC-Server stores the Subject, Date and Sender not as Header-Line but
only in the ENVELOPE-Line.

I want now to repair these Headers with the corresponding fields from
the Envelope with offlineimap (the only program i got to work with this
server). But I think I have to modify the code of offlineimap itself,
but I don't have a clue where to start. Could someone help me on this way?

Kind regards,
Henning