Extending Outlook PST sizes

In Outlook 2003 and Outlook 2007, the maximum size of an Unicode Outlook PST file has been limited to 20GB. As of Outlook 2010 and 2013, this limit has been set to 50GB. [Unsure about Outlook 2016 but do you really need more? :-)]

You can increase (or decrease) this limit via the Registry or via Group Policies. The maximum size can be set as high as 4TB [that’s “ffffffff” in hex – you will see why below].

In the registry, go to the appropriate registry path….

  • 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

You need to create and set two DWORD values:

  • 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 keys are case sensitive.
  • MaxLargeFileSize must be at least 5% larger than WarnLargeFileSize.
  • You can’t use these settings with an ANSI Outlook 97-2002 formatted PST file. Unsure which you are using? Open the properties of the PST file. Look at the “Format:” field. If it says Personal Folders File or Outlook Data File, it means that you are in Unicode format. Otherwise, you are using the ANSI format. The ANSI code would be more likely to be there if you’ve used Outlook for the last 12+ years with your account.

About ebraiter
computer guy

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