How to increase Size of OST in Cached Exchange mode on Outlook 2003

Posted on 2009-02-17
Last Modified: 2012-05-06
I am hitting a 4GB limit with outlook.ost in cached mode.
Note: The machine in question has NTFS file system, not FAT32. Hence this is not the same as

Question by:thehagman
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    Author Comment

    The links you gave do not work, even after trying to repair wrapping effects. Googling for Templeton Sweetman.ppt, there seem to be many bad links to that presentation...

    Meanwhile I've followed this:
    There was no setting before, so the active limit *should* have been 20GB.

    I renamed the *.ost, set MaxLargeFileSize to 0x5000 and WarnLargeFileSize to 0x4c00 and hope that at least after explicitly stating them, the default values take effect.
    It may take a while until I can report more on this as right now the box is pulling from the Exchange server
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    When Cached Exchange Mode first creates a local copy of a user's mailbox, the user's current OST file  if one exists  is updated. When users have relatively small mailboxes  for example, less than 500 megabytes (MB) of Exchange Server data  this works fine. However, ensure that users with larger mailboxes have Unicode-formatted OST files  the new file format in Outlook 2003  before deploying Cached Exchange Mode. Unicode OST files can store up to 20 gigabytes (GB) of data, instead of the limit of 2 GB on non-Unicode (ANSI) Outlook files.

    By creating Unicode OST files, you can help avoid error messages for users that result when Outlook runs out of OST file space when attempting to create a local copy of the user's mailbox for Cached Exchange Mode. Outlook with Cached Exchange Mode also works better when there is plenty of free space in the user's OST file  for example, when only 5 to 10 percent of a 20 GB OST file is used.

    Also be sure that users' OST files are located in a folder with sufficient disk space to accommodate users' mailboxes. For example, if users' hard drives are partitioned to use a smaller drive for system programs (the system drive is the default location for the folder that contains the OST file), specify a folder on another drive with more disk space as the location of users' OST files
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