In Outlook, what is Cached Exchange Mode, and how do I enable or disable it?

Cached Exchange Mode, available in Outlook 2010, 2007, and 2003, is similar to offline folders in previous versions of Outlook, though easier to use. (For more, see In Microsoft Outlook for Windows, what are offline folders, and how do I enable and disable them?) Cached Exchange Mode allows you to work with your Exchange account data when your connection to the Exchange server is interrupted or unavailable. Cached Exchange Mode stores a copy of your mailbox on your computer by automatically creating and using an offline folder file (an .ost file), into which it downloads and maintains a synchronized copy of the items in all the folders of your mailbox. Outlook automatically manages your server connection and data updates; when your connection is restored, Outlook synchronizes your cached mailbox with your mailbox on the server.

However, you still have the option to manually set the connection behavior in order to control the amount of data transmitted to or from the Exchange server. For example, if you use a service that charges you by the amount of data you send and receive (common with cellular and GPRS connections), you can select the Download Headers option to minimize the amount of data sent over the connection, and reduce your connection time. From the headers, you can choose the full items you need.

Note: If you use third-party applications that interface with your Outlook profile (e.g., PDA synchronization software, spam filtering software, Outlook add-ins), UITS recommends that you research these applications to make sure they are compatible with Cached Exchange Mode before enabling it.

To enable or disable Cached Exchange Mode:

Outlook 2010 and 2007

1. In 2010, from the File tab, under "Account Information", click Account Settings, and then choose Account Settings... .

   In 2007, from the Tools menu, select Account Settings... .

2. Highlight your Exchange server account, and then click Change... .
   
   
3. To turn Cached Exchange Mode on or off, under "Microsoft Exchange Server:", check or uncheck Cached Exchange Mode. Click Next, and in the window that opens, click OK.
   
   
4. Click Finish. Restart Outlook for the change to take effect.

Outlook 2003

1. From the Tools menu, select Email Accounts... .
   
   
2. In the window that opens, under "Email", make sure View or change existing email accounts is selected, and then click Next.
   
   
3. Highlight your Exchange server account, and click Change... .
   
   
4. To turn Cached Exchange Mode on or off, under "Microsoft Exchange Server:", check or uncheck Cached Exchange Mode. Click Next, and in the window that opens, click OK.
   
   
5. Click Finish. Restart Outlook for the change to take effect.

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