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Outlook Data Files (.pst and .ost)

There are two types of Outlook Data Files used by Outlook. An Outlook Data File (.pst) is used for most accounts. If you are using a Microsoft Exchange account, your items are usually delivered to and saved on the mail server. To allow you to work with your messages even when you can’t connect to the mail server, a second type of data file that is named an offline Outlook Data File (.ost) is kept on your computer.

The primary differences between the two types of Outlook data files are as follows:

Outlook Data Files (.pst) are used for POP3, IMAP, and web-based mail accounts. When you want to create archives or back up your Outlook folders and items on your computer, such as Exchange accounts, you must create and use additional .pst files.

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 have to be backed up like Outlook Data Files (.pst).

Location
Outlook Data Files (.pst)

Note: Microsoft Exchange Server accounts save your information on the mail server. To use Cached Exchange Mode or to work offline, copies of your items are saved in an offline Outlook Data File (.ost). See the Outlook Data Files (.ost) section for more information. Also, some organizations allow you to export or archive your items to a .pst file.

The fastest way to open the folder where your Outlook Data File (.pst and .ost) is saved is to do the following:

  1. In Outlook 2010, click the File tab.
  2. Click Account Settings, and then click Account Settings.
  3. On the Data Files tab, click an entry, and then click Open Folder Location.

Outlook Data Files (.pst) created by using Outlook 2010 are saved on your computer in the Documents\Outlook Files folder. If you are running Windows XP, these files are created in the My Documents\Outlook Files folder.

If you upgraded to Outlook 2010 on a computer that already had data files that were created in earlier versions of Outlook, these files are saved in a different location in a hidden folder.

Windows 7 and Windows Vista     drive:\Users\user\AppData\Local\Microsoft\Outlook

Windows XP     drive:\Documents and Settings\user\Local Settings\Application Data\Microsoft\Outlook

Tip:  For information about hidden folders in Windows, see Windows Help and Support.

Outlook Data File (.ost)

The .ost file is synchronized with the items on the server that runs Exchange. Because your data remains on the Exchange server, you can re-create this .ost file on your new computer without having to back up the .ost file.

Windows 7 and Windows Vista     drive:\Users\user\AppData\Local\Microsoft\Outlook

Windows XP     drive:\Documents and Settings\user\Local Settings\Application Data\Microsoft\Outlook