Increase maximum size pst-files

How do I increase the maximum file size of an UNICODE pst file? The default size is 20 GB but as far as I know there must be a registry value that allows to increase the maximum up to approximately 4TB.

Yes, you can do this via the registry or via Group Policies. The default maximum size for pst-files in Outlook 2010 is 50GB.

Note: This tip does not apply to pst-files who are in the Outlook 97-2002 format (ANSI formatted pst-files).

Via the Registry
You need to go to the following location in the registry;
Outlook 2003: HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\PST
Outlook 2007: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PST
Outlook 2010: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\PST

Here you must create and set 2 new DWORD values (note that these values are case senstive);

• WarnLargeFileSize
  Don’t set this higher than 4090445042 (decimal) or f3cf3cf2 (hexadecimal)
• MaxLargeFileSize
  Don’t set this higher than 4294967295 (decimal) or ffffffff (hexadecimal)

The first value is how many MB a user can write to a pst-file. The second value is how many MB the system can write to a pst-file. This difference has to be at least 5% since there is more written to a pst-file than just user data.

Via Group Policies
Not comfortable editing the registry? You can then use Group Policies as well even when you are on a home computer. For instructions on how to use Group Policies see this guide.
The settings for adjusting the pst filesize can be found in the section Miscellaneous-> PST Settings. The following 2 settings need to be modified;

• Large PST: Absolute maximum size
  Don’t set this higher than 4294967295
• Large PST: Size to disable adding new content
  Don’t set this higher than 4090445042