How to Configure the Size Limit of .PST and .OST Files in Outlook

MS Outlook supports OST and PST file for email storage and there is a size limit in these files. In case the size is exceeded beyond the limit, the possibility of file corruption has increased so it is better to set PST size limit and set OST size limit on Outlook. MS Outlook 2003, 2007, 2010, and 2013 support ANSI and UNICODE Offline folders (OST) as well as personal folders (PST). In this article, we will get to know that how to we can use the following registry entries to limit the size of OST and PST files.

According To Outlook 2010 and Outlook 2013

  • The WarnFileSize registry entry (Default value: 1.816 GB
  • The WarnLargeFileSize registry entry (Default value: 47.5 GB)
  • The MaxFileSize registry entry (Default value: 1.933 GB
  • The MaxLargeFileSize registry entry (Default value: 50 GB)

According To Outlook 2007 and Outlook 2003

  • The WarnFileSize registry entry (Default value: 1.816 GB)
  • The WarnLargeFileSize registry entry (Default value: 19 GB)
  • The MaxFileSize registry entry (Default value: 1.933 GB)
  • The MaxLargeFileSize registry entry (Default value: 20 GB)

Note: Always remember that The WarnFileSize registry do not allow outlook to warn you before the size limit of the file is exceeded form limit.

The WarnFileSize Registry Entry: This registry entry determines the maximum data storage limit that a PST and OST files can contain. When this PST and OST file size limit has reached, these files are not allowed to add any more data. However, the physical file size can still increase as it has its own internal process.

The MaxFileSize Registry Entry: This registry files limit the maximum size of both PST and OST files and determines the maximum limit of growth. When this maximum size is reached to its limit then Outlook does not allow the file size to grow more.

Here is the process by which you can limit the size of your OST and PST files:

  1. On Windows screen click ‘Start’ button and then select ‘Run’
  2. An box will open, now type ‘regedit’ and then click OK
  3. Expand ‘My Computer’ option, available on the left pane, and then expand HKEY_CURRENT_USER.
  4. Expand ‘Software’ and then expand ‘Policies’.
  5. Now expand ‘Microsoft’ and then expand ‘Office’
  6. Now expand 15.0 for Outlook 2013, 14.0 for Outlook 2010, 12.0 for Outlook 2007, or 11.0 for Outlook 2003, and then click Outlook.
  7. Now click PST and then in the right pane right click MaxFileSize
  8. Select Modify and type value in the Value data box.
  9. Click OK
  10. Similarly, you can right click on WarnFileSize, MaxLargeFileSize, WarnLargeFileSize, and repeat the above steps.

In case, the registry values do not exist and you have to create them, follow the below mentioned steps to create registry values.

1. On Windows screen click ‘Start’ button and then ‘Run’, now type Regedit on the type box on the left pane and expand the following registry key:
For Outlook 2003


For Outlook 2007


For Outlook 2010


For Outlook 2013


2. Now click Edit menu and select ‘New’ and then click ‘Key’

3. Type PST and press Enter key

4. Go to Edit menu and point New, now click DWORD value

5. Write MaxFileSize, and then press Enter key twice

6. In the Edit DWORD Value window, enter a value in the required box and click OK

7. Now, to create another DWORD WarnFileSize, repeat the above-mentioned steps 2 to 6

8. Similarly to create another DWORD MaxLargeFileSize repeat 2 to 6 steps
9. Repeat steps 2 to 6, to create another DWORD WarnLargeFileSize

10. Now, close the registry

Note: The ORK tool can be used for mass deployment of these registry keys on end-user machines.

The steps that we have discussed are applied to both .pst and .ost files. Any kind of modification with these registry values can affect .ost files that are psed with AutoArchive, with .pst and with CEM (Cached Exchange Mode) files. In case your Outlook is configured to download shared folders, then it will use .ost file to store content. If this shared folder consists of many large files and attachments, the size of it will grow extremely.

However, Outlook 2013 has introduced support for Site Mailbox. If any Outlook 2013 user is using Microsoft Exchange Server 2013/Microsoft SharePoint 2013 and is granted permission to a site mailbox, then the site mailbox will be automatically added to the Outlook 2013. In case the download shared folders are enabled, then the site mailbox data are synchronized to .ost file. It will exceed the set limit of local .ost file.

The above-mentioned steps will explain you that how to modify the registry. However, any incorrect step or process may create serious problems at the time of registry modification, so always follow all the steps carefully. For more safety, you can take backup of your registry before any modification applies to it so that you can restore it if any problem occurs.

If the MaxFileSize registry value entry exceeds the ANSI 2 gigabyte (GB) limit on any of the .ost or .pst files. It will automatically ignore the next value, to prevent the file from corruption. For a UNICODE file, the WarnFileSize registry entry default value is calculated to be 95% of the MaxFileSize registry entry, and it remains at 1,950,368,768 bytes for small ANSI files. However, you can set the UNICODE limits beyond the default values, but it can reduce the performance of the file.

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