Maximum Mailbox Size

For Outlook 2003 and 2007 the maximum PST and OST file size is limited to 20GB.
For Outlook 2010, 2013 and 2016 this limit has increased to 50GB.
This can be altered via the Registry or Group Policy.

Cause:
User has reached their maximum mailbox size and do not want to delete any emails.

Solution:

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:
This example increases the limit to 100GB and warns at 95GB.

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

Group Policy:

Open Group Policy Editor and go to User Configuration > Administrative Templates > Microsoft Outlook <version> > Miscellaneous > PST Settings

Modify the following 2 settings:

• 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