The Limit for Outlook OST Files

How big can your Outlook OST file grow for cached Exchange mode?  Well the answer to this is BIG.  Outlook 2003/2007 out of the box has a 20GB limit on OST files, while Outlook 2010 has a 50GB limit on OST files.

This is documented by Microsoft on the following KB article:

http://support.microsoft.com/kb/832925

Whilst these limits have been put in place they can be extended by modifying the MaxLargeFileSize DWORD registry value located under the following location:

Outlook 2010

The policy location for the registry entries is located in the following path in Registry Editor:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\PST

The user preference location for the registry entries is located in the following path in Registry Editor:

HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\PST

Outlook 2007

The policy location for the registry entries is located in the following path in Registry Editor:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook\PST

The user preference location for the registry entries is located in the following path in Registry Editor:

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PST

Outlook 2003

The policy location for the registry entries is located in the following path in Registry Editor:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Outlook\PST

The user preference location for the registry entries is located in the following path in Registry Editor:

HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\PST

So whats this harp about PST files and OST files limited to 2GB in size?  ANSI (the format previously used for OST/PST files) is limited to 2GB in size - and it does not handle hitting this limit very well.

The new format which is used is Unicode - the actual Unicode limit is unknown.  We do believe it is in the TB, perhaps around 4 TB, but we have never tested (nor have we ever been able to test) to find the limit for performance reasons.