How to configure the size limit for both (.pst) and (.ost) files in Outlook 2007 and in Outlook 2003

Microsoft Office Outlook 2007 and Microsoft Office Outlook 2003 supports both American National Standards Institute (ANSI) and UNICODE personal folders (.pst) and offline folder (.ost) files. This article describes how to use the following four registry entries to limit the size of both the .pst and the .ost files:

• The MaxFileSize registry entry
• The WarnFileSize registry entry
• The MaxLargeFileSize registry entry
• The WarnLargeFileSize registry entry

Note The WarnLargeFileSize and WarnFileSize registry entries do not enable Outlook to warn you before the file size limit is reached.

The MaxFileSize registry entry

The MaxFileSize registry entry determines the absolute maximum size that both the .pst and the .ost files can grow to. After this maximum size is reached, Outlook does not permit the size of the file to grow beyond this size.

The WarnFileSize registry entry

The WarnFileSize registry entry determines the maximum data that both the .pst and the .ost files can have. After this maximum data is reached, neither the .pst nor the .ost files are permitted to add any more data. However, the size of the physical file may still increase because of internal processes.

In the following table, the MaxLargeFileSize registry entry and the WarnLargeFileSize registry entry refer to a UNICODE formatted (new Large format) file, and the MaxFileSize registry entry and the WarnFileSize registry entry refer to an ANSI formatted (an earlier Microsoft Outlook format) file. The UNICODE values are set in megabyte (MB) increments, while the ANSI values are set in byte increments.The policy location for the registry entries is located in the following path in Registry Editor.

Outlook 2007

The user preference location for the registry entries is located in the following path in Registry Editor:

Outlook 2003

The user preference location for the registry entries is located in the following path in Registry Editor:

Follow these steps to configure the size limit for both the .pst and the .ost files.

Note The settings that are discussed in this article apply to both .ost and .pst files. If you modify these registries, this can affect .ost files that are used with Cached Exchange Mode, with AutoArchive, and with .pst. files.

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

1. Click Start, and then click Run.
2. In the Open box, type regedit, and then click OK.
3. In the left pane, expand My Computer, and then expand HKEY_CURRENT_USER.
4. Expand Software, and then expand Policies.
5. Expand Microsoft, and then expand Office.
6. Expand 11.0 for Outlook 2003 and 12.0 for Outlook 2007, and then expand Outlook.
7. Click PST, and then right-click MaxFileSize in the right pane.
8. Click Modify, and then type the value in the Value data box.
9. Click OK.
10. Right-click WarnFileSize, and repeat steps 8 through 9.
11. Right-click MaxLargeFileSize, and repeat steps 8 through 9.
12. Right-click WarnLargeFileSize, and repeat steps 8 through 9.

Note You may have to create the registry values if they do not exist. If the registry values do not exist, follow these steps to create them.

1. Click Start, click Run, type Regedit, and then click OK.
2. In the left pane, expand following registry key:
   
   For Outlook 2007
   HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook
   For Outlook 2003
   HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Outlook
3. On the Edit menu, point to New, and then click Key.
4. Type PST, and then press ENTER.
5. On the Edit menu, point to New, and then click DWORD value.
6. Type MaxFileSize, and then press ENTER two times.
7. In the Edit DWORD Value window, type the value in the Value data box, and then click OK.
8. Repeat steps 3 through 7 to create another DWORD WarnFileSize.
9. Repeat steps 3 through 7 to create another DWORD MaxLargeFileSize.
10. Repeat steps 3 through 7 to create another DWORD WarnLargeFileSize, and then close the registry.
    
    Note For mass deployment of these registry keys on end-user machines, the ORK tool can be used.

To automate the registry creation on end-user machines, use ORK for deployment scenarios.
It is recommended that the values between the MaxFileSize registry entry and the WarnFileSize registry entry, and the values between the MaxLargeFileSize registry entry and the WarnLargeFileSize registry entry be at least 5 percent (%) so that internal processes are not hindered from continuing.

If the value of the MaxFileSize registry entry ever exceeds the ANSI 2 gigabyte (GB) limit on either the .pst or the .ost files, the value will be ignored to limit the size to 2 GB to prevent corruption. The default value for the WarnFileSizeregistry registry entry is calculated to be 95% of the MaxFileSize registry entry for a UNICODE file, and it remains at 1,950,368,768 bytes for small ANSI files.

Note You can set the UNICODE limits beyond the values that are listed in the table. However, we do not recommend doing this because performance can decrease.

If .ost files or .pst files reach the limit that is specified in the WarnFileSize or the WarnLargeFileSize registries, the compaction function is triggered to try to reduce the size of the file to a usable level. When the WarnFileSize or the WarnLargeFileSize limit is reached, e-mail messages cannot be sent (provided that sent e-mail messages are stored in the Sent Items folder), and items cannot be copied or moved within the file. If the file is an archive .pst file that is used for AutoArchive, the AutoArchive operation will fail. However, e-mail messages can be deleted or archived from a .pst or from an .ost file that is currently being used as the default delivery location.

The following are some of the errors that may occur when files reach the maximums specified in the registries:

• When you try to move items to a .pst or an .ost file that has reach the limit, you receive the following error message:
  Can't move the items. The file <path>\<filename>.pst has reached its maximum size. To reduce the amount of data in this file, select some items that you no longer need, and then permanently delete them.
• When e-mail messages are delivered to a .pst or an .ost file that are using Cached Exchange Mode, and the file has reached the limit, the Mailbox Cleanup wizard launches.