Strange behavior when syncing two IMAP servers

[Matthieu Rakotojaona]

Hello everyone !

I am working on an IMAP server of my own. I'm trying to sync it with a
GMail account, with a nametrans.

System : Linux 3.1.1, OfflineIMAP v.6.3.4

When I add a message to a mailbox on my side and want to sync
(upstream), here is the behavior I see on my side, on the IMAP server:

1) SELECT, EXAMINE, FETCH FLAGS, SELECT, EXAMINE the mailbox
2) FETCH BODY.PEEK[] the new email
3) SELECT the mailbox
4) APPEND the exact same email
5) CHECK, SELECT the mailbox
6) DELETE (STORE +FLAGS \Deleted) the email (the one that was read,
not the one that was appended)
7) SELECT, EXPUNGE the mailbox

So, I have a few questions :

* My custom server cannot append a message if it already exists. Why
does it append exactly the same, to remove the first one ?
All I can see from this is that the email should get a new UID, but I
can't see the reason. And it doesn't serves my purpose =]

* Where can I see the relevant parts (2, 3 ( I suppose OfflineIMAP
verifies some things at that moment), and 4) in the code ? I couldn't
find them.

Thank you !

-- 
Matthieu RAKOTOJAONA