Reduce the size of Outlook Data Files (.pst and .ost)

Your Microsoft Outlook mailbox grows as you create and receive items. When you delete items, the size of the Outlook Data File (.pst and .ost) file might not decrease in proportion to the data that you deleted. There are several ways to manage your mailbox and reduce the size of the data file.

What do you want to do?


Manage your mailbox

The Mailbox Cleanup tool is used to view the size of your mailbox and individual folders. You can also archive older items to an archive Outlook Data File (.pst) (Outlook Data File (.pst): Data file that saves your messages and other items on your computer. You can assign a .pst file to be the default delivery location for email messages. You can use a .pst to organize and back up items for safekeeping.) and empty your Deleted Items folder.

  1. Click the File tab.
  2. Click Cleanup Tools.
  3. Click Mailbox Cleanup.
  4. Do any of the following:
    • To view the total size of your mailbox and any individual folders it contains, click View Mailbox Size.
    • To locate older items, select Find items older than n days, enter a number between 1 and 999, and then click Find.
    • To locate large items, select Find items larger than n kilobytes, enter a number between 1 and 9999, and then click Find.
    • To move older items in your mailbox to an archive Outlook Data File (.pst), click AutoArchive.

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

  • To view the size of your Deleted Items folder, click View Deleted Items Size.
  • To empty your Deleted Items folder, click Empty.
  • To view the size of your Conflicts folder, click View Conflicts Size.
  • To delete the contents of your Conflicts folder, click Delete.

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Reduce the size of an Outlook Data File (.pst)

If you delete items from an Outlook Data File (.pst), the file is automatically compacted in the background when you’re not using your computer and Outlook is running. You can also manually start the compact command immediately. It might take several minutes to compact an Outlook Data File (.pst).

  1. Delete any items that you do not want to keep.
  2. Open the Folder List view. At the bottom of the Navigation Pane (Navigation Pane: The column on the left side of the Outlook window that includes buttons for the Mail, Calendar, and Tasks views and the folders within each view. Click a folder to show the items in the folder.), click the Folder List icon or press CTRL+6.
  3. In the Navigation Pane, right-click the Deleted Items folder, and then click Empty Folder.
  4. Click the File tab.
  5. Click Account Settings, and then click Account Settings.
  6. On the Data Files tab, click the data file that you want to compact, and then click Settings.
  7. Click Compact Now.

 Note    You do not have to exit Outlook after you compact an Outlook Data File (.pst) file.

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Reduce the size of an offline Outlook Data File (.ost)

An offline Outlook Data File (.ost) is exclusive to Microsoft Exchange Server accounts. Reducing the size of an offline Outlook Data File (.ost) might improve performance if you have deleted many items (item: An item is the basic element that holds information in Outlook (similar to a file in other programs). Items include e-mail messages, appointments, contacts, tasks, journal entries, notes, posted items, and documents.). This procedure does not delete any items saved on the computer running Microsoft Exchange Server.

  1. Delete any items that you do not want to keep.
  2. Open the Folder List view. At the bottom of the Navigation Pane (Navigation Pane: The column on the left side of the Outlook window that includes buttons for the Mail, Calendar, and Tasks views and the folders within each view. Click a folder to show the items in the folder.), click the Folder List icon or press CTRL+6.
  3. In the Navigation Pane, right-click the Deleted Items folder, and then click Empty Folder.
  4. Click the File tab.
  5. Click Account Settings, and then click Account Settings.
  6. On the Data Files tab, click the data file that you want to compact, and then click Settings.
  7. Click Compact Now.


 Notes 

  • To delete an item from both the online and offline folders, select the item, and then press DELETE.
  • If you are using an Exchange account in Cached Exchange Mode, only the selected folder will be cleared from the offline Outlook Data File (.ost). The items on the server will be downloaded again to the .ost file on the next synchronization, if the folder is selected under Folder Options in Send/Receive Settings for the Exchange Server e-mail account.
  • When you use Cached Exchange Mode, public folders favorites are not synchronized by default. If you choose to synchronize public folders, the size of your offline Outlook Data File (.ost) might increase significantly.

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Applies to:
Outlook 2010