No. What I'm saying is that when you make a PST file your default delivery location, a number of not exactly nice things happen:
-- Unless you are meticulous about making your own backups, the data in the .pst file won't be backed up like data in your Exchange mailbox is. Therefore, if your .pst file becomes corrupted, your data is lost.
-- When you accept meeting requests or click the New | Appointment command to create a new appointment, those appointments go into the Calendar folder in your .pst file. The Calendar folder in your mailbox remains empty, unless you explicitly create an appointment in that folder, and thus no one in your organization has an accurate picture of your free/busy availability.
-- You can't access your Outlook data from any other machine on the company network or from outside the company using Outlook Web Access, because it's not on the server. It's in the local PST file.
If the mailbox size limit is an issue, then the better question to ask would be, How can I keep my mailbox down to the allowed size and still have access to all the data I need? The exact answer is going to depend on what that key data consists of. Automatic archiving of older data and Rules Wizard rules are two important tools that can help you put some data into .PST files while not abandoning the features of the Exchange mailbox.
What Cached Exchange mode adds, BTW, is the maintenance of a replica of your mailbox on the local hard drive so that you can keep working if the network connection to your Exchange mailbox is broken for any reason. You also get junk mail processing and generally faster performance, because Outlook doesn't have to go to the server for things like the address book.
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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers