Imagine the following scenario: MS Outlook with multiple mail accounts and additionally one MS Exchange server. Therefore, you know two options exist: On the one hand, prefer the MS Exchange server and hold all your mails there or on the other hand, keep your local personal folder for mail incoming. But if you only use IMAP accounts, the local personal folder will be clear, expect one PST-file via IMAP server. In this case, using the local personal folder for incoming mail spams up your clear local incoming folder and removes incoming mails from the MS exchange server completely to your local PST-file.
That is not, what you really what, because the existence of the MS Exchange is more or less ignored (expecting for tasks and meetings).
If you select to change your incoming mail folder to the MS Exchange server, you keep your mail received via MS Exchange server on the server. Additionally, your local PST-file remains almost clear, especially because of the empty incoming mail folder.
Why is this not the optimal solution? It’s almost quite good, but if you’re sending a mail, copies will be kept per default in the sent folder, this remains now on the MS Exchange server, thus you mix your IMAP-sent mail with your MS Exchange mails.
But, this is quite simple to solve.
Step 1: Create a local (client-side) manual mail rule via menu item tools. Specify that all outgoing mails should be copied to a specific folder, and define your local sent-items folder as destionation.
Step 2: Go to tools » options » preferences » e-mail-options » advanced e-mail options and uncheck the second entry, “In folders other than the Inbox, save replies with original message”.
Thus, Outlook will not copy sent items to the MS Exchange folder sent items, but you store a copy of all sent items in your local folder sent items (information hiding from the MS Exchange server). No sent items will be mixed with your private ones 🙂
Update: Because of the fact, that the reminder service is not able to serve events from both/multiple calendars (not implemented yet?) the following decision may be better. Change incoming folder for mails to your local PST-file. Thus, the MS Exchange server will be enabled in _slave_ mode. The problem of moving the incoming MS Exchange messages to your local incoming mails folder can be handled by creating a rule, moving all incoming mails to a separate folder on the MS Exchange server, e.g. Incoming. Therefore, the MTA will always find an empty default incoming mail folder on the MS Exchange server and will not try to download new items to your local file.