Syncing Thunderbird 2.0 mailbox with Blackberry for an Exchange account

My organization uses Microsoft Exchange as the Mail Server and a BES server to sync mails on my blackberry.

The mailbox on server is allowed only 50 MB of space and thus I need to continuously delete mails on the server. Previously I used POP to fetch mails from Exchange to Thunderbird mail client but this had sync issues (mails were downloaded multiple times, the read/unread information was different on mobile and desktop) once I configured my Blackberry using BES.

I recently shifted from POP to IMAP (had to get IMAP enabled from the administrator) and this has solved a number of problems.

I've created filters which automatically shift few mails to the local folders and I manually move emails to local folders whenever required. The move operation does not automatically compact (delete emails on mailbox which were moved/deleted locally) folders but the following will make that happen:

Goto Edit -> Preferences -> Advanced -> General -> Config Editor and then make the mail.imap.expunge_after_delete option as 'true'. Restart Thunderbird to use this config.

Secondly, I wanted the sent mails to be saved on the 'Sent Items' folder on the Exchange Server's mailbox. This can be achieved by subscribing to the 'Sent Items' folder and placing a copy of send messages in the 'Sent Items' folder. To achieve this:

1) Right click on the 'Inbox' for the IMAP account and click 'Subscribe'. Select the 'Sent Items' folder. You should now see the folder next to Inbox on the left panel.

2) Goto Edit -> Account Settings -> Copies & Folders and select 'Sent Items' as the Other folder under 'when sending messages, automatically' -> 'Place a copy in'.