: By default, when you add an account that uses an offline Outlook Data File (.ost), the file is automatically created and data from the server is downloaded. Also, if you specify a new folder location for the offline Outlook Data File (.ost), a new file is automatically created. Although not required, you can manually move the existing file to the new folder to avoid the download time that is required to re-create the file.
Outlook Data Files (.ost) are used when you have an Exchange account and want to work offline or use or use the default Cached Exchange Mode. This type of data file is also used for accounts that you set up with the Outlook Connector for Outlook.com (formerly Hotmail). Outlook Data Files (.ost) are always copies of items that are saved on a mail server and don’t need to be backed up like Outlook Data Files (.pst).
Re-create an offline Outlook Data File (.ost)
Offline Outlook Data Files (.ost) are copies of your Exchange information. It is not necessary to back up this file. You can create a new copy at any time.
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Exit Outlook.
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In Control Panel, click or double-click Mail.
Where is Mail in Control Panel?
Mail appears in different Control Panel locations depending upon the version of the Microsoft Windows operating system, Control Panel view selected, and whether a 32- or 64-bit operating system or version of Outlook is installed.
The easiest way to locate Mail is to open Control Panel in Windows, and then in the Search box at the top of window, type Mail. In Control Panel for Windows XP, type Mail in the Address box.
: The Mail icon appears after Outlook starts for the first time.
The title bar of the Mail Setup dialog box contains the name of the current profile. To select a different existing profile, click Show Profiles, select the profile name, and then click Properties.
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On the E-mail tab, select the Exchange account, and then click Change.
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Clear the Use Cached Exchange Mode check box.
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Click More Settings.
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On the Advanced tab, click Offline Folder File Settings.
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Click Disable Offline Use, and then in the dialog box that appears, click Yes.
: If you cannot click Disable Offline Use, this indicates the Use Cached Exchange Mode check box was not cleared in step 4. This check box must be cleared.
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Again, click Offline Folder File Settings.
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Click OK.
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In the dialog box that appears, click Yes.
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Under Cached Exchange Mode Settings, select the Use Cached Exchange Mode check box.
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Click OK, click Next, and then click Finish.
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In the Account Settings and Mail Setup dialog boxes, click Close.
