In Outlook 2003 and Outlook 2007, the maximum size of a Unicode pst-file has been limited to 20GB. In Outlook 2010, 2013 and 2016, this limit has been set to 50GB.

You can increase (but also decrease) this limit via the Registry or via Group Policies.

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

Via the Registry:

To increase the maximum size of a pst-file in Outlook, you’ll need to create and set 2 values in 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

Outlook 2013
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\PST

Outlook 2016
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST

The following 2 new DWORD values must be created or set;

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 before receiving a warning that the file is full. 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:

The settings for adjusting the pst file size 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