Reduce the size of Outlook data files

Your Microsoft Outlook mailbox grows as you create and receive items. Even when you delete items, the size of your data file might not decrease in proportion to the amount of 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 the size of your mailbox

You can use the Mailbox Cleanup tool, which allows you to view the size of your mailbox and individual folders. You can also archive older items to an archive Personal Folders file (.pst) and empty your Deleted Items folder.

  1. On the Tools menu, click Mailbox Cleanup.
  2. Do any of the following:
    • To view the total size of your mailbox and of individual folders within it, 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 Personal Folders file (.pst), click AutoArchive. The default folder for archive .pst files is c:\Documents and Settings\user name\Local Settings\ Application Data\Microsoft\Outlook.
    • 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 a Personal Folders file (.pst)

If you delete items from a Personal Folders file (.pst), the file is automatically compacted in the background when you’re not using your computer and Outlook is running. If you want to immediately reduce the size of the file, you can force a compaction. The procedure to compact the data file might take several minutes.

  1. On the File menu, click Data File Management.
  2. Click the data file that you want to compact, and then click Settings.
  3. Click Compact Now.

 Note    You do not have to exit Outlook after you compact a .pst file.

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Reduce the size of the Offline Folder file (.ost)

Reducing the size of the Offline Folder file (.ost) (Offline Folder file: The file on your hard disk that contains offline folders. The offline folder file has an .ost extension. You can create it automatically when you set up Outlook or when you first make a folder available offline.) file may improve performance if you have deleted a large quantity of 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 that are saved on the server.

  1. Delete any items that you do not want to keep, and then empty the Deleted Items folder.
  2. On the Tools menu, click Account Settings.

ShowThe Account Settings command is missing.

The Account Settings command is on the Tools menu in Microsoft Office Outlook 2007. If you are using an earlier version of Outlook, the following instructions do not apply. Use the Help that is included with that product. If the title bar of the program that you are using displays Microsoft Outlook Express, you are using a program that is not the same as Outlook. See Help in Outlook Express for assistance.

  1. In the list, select Microsoft Exchange Server, and then click Change.
  2. Click More Settings.
  3. Click the Advanced tab, and then click Offline Folder File Settings.
  4. 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 local .ost file. 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 Folder file (.ost) may increase significantly.

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Applies to:
Outlook 2007