Move an offline Outlook Data File (.ost)

When you use a Microsoft Exchange Server account and turn on offline support or use Cached Exchange Mode, a synchronized copy of your Microsoft Outlook items is saved in an offline Outlook Data File (.ost) (offline Outlook Data File (.ost): The file on your hard disk that contains a copy of mail messages and Outlook items. The file is synchronized with the information saved on a mail or Exchange server. The offline Outlook Data File has an .ost extension.) in a hidden folder on your computer.

 Note    A Microsoft Exchange Server account is required.

ShowWhere is my Outlook Data File (.ost)?

  1. Click the File tab.
  2. Click Account Settings, and then click Account Settings.
  3. Click the Data Files tab.

The Outlook Data File (.ost) location appears in the Location column for the Exchange account.


You can change where the offline Outlook Data File (.ost) file is saved, such as a different folder or hard disk. When you specify a new folder, you do not have to back up the existing file or move it to the new folder.

By default, when 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.

 Important    These steps shouldn’t be used for moving an offline Outlook Data File (.ost) to another computer. When you add an Exchange account in Outlook on another computer and then work offline or use Cached Exchange Mode, an offline Outlook Data file (.ost) is automatically created and your Outlook data is downloaded.

The following steps change the folder location and create a file or move the existing one.

 Note    An offline Outlook Data File (.ost) is also used for the Outlook Connector . These files cannot be moved.

  1. Exit Outlook.

If you want to move the existing file, open Windows Explorer and do so now. See the introduction for the default file location. Note that moving the file isn't required as it can be automatically recreated in the new location.

  1. In Control Panel, click or double-click Mail.

ShowWhere 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 2010 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.

 Note    The Mail icon appears after Outlook starts for the first time.

  1. Click Show Profiles, click the profile that contains the Exchange account, and then click Properties.
  2. Click Data Files, click the Exchange account, and then click Settings.
  3. On the Advanced tab, clear the Use Cached Exchange Mode check box, and then click OK.

The following message appears: You must restart Outlook for these changes to take effect.

  1. Click OK.
  2. Again, click Settings, and then on the Advanced tab, click Outlook Data File Settings.
  3. Click Disable Offline Use, and then click Yes in the dialog box that appears.

 Note    If the Disable Offline Use button is grayed out, this indicates the Use Cached Exchange Mode check box was not cleared in step 5. This check box must be cleared first.

  1. Again, click Outlook Data File Settings.
  2. Do one of the following:
    • I want to create a file (default)     Click Browse, select the folder where you want to save the offline Outlook Data File (.ost), and then click Open.
    • I want to move the old file     Click Browse, select the offline Outlook Data File (.ost) that you moved to a new folder location, and then click Open.
  3. Click OK.
  4. Select the Use Cached Exchange Mode check box, and then click OK.

You receive the following message: You must restart Outlook for these changes to take effect

  1. Click OK.
  2. In the Account Settings and Mail Setup dialog boxes, click Close.
  3. In the Mail dialog box, click OK.

 Note    When an offline Outlook Data File (.ost) is created, the old file is not deleted. To increase available hard disk space, delete the old file.

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Applies to:
Outlook 2010