3 Replies Latest reply: Oct 20, 2012 1:29 AM by TechPro RSS

Source One users and large OST file not shrinking


Our users are not seeing a reduction of OST files after Source one short cuts the mailbox.

Anyone have any tricks here to reduce the size of ost? other than manual compact of ost file.

WHy is the ost file not reduced when the mailbox size is shrinking?



  • 1. Re: Source One users and large OST file not shrinking
    Deanna Hoover



    The offline access guide that is posted on PowerLink explains how Offline Access works with the OST files. Basically,

    The Offline Access Agent on the user’s computer synchronizesthe OA cache with the OST file.

    shortcut messages are created in the user’s mailbox on the Exchange server and replicated to the OST file on the user’s



    Cache settings can be modified and the details of how configure cache is documented in the offline accesss users guide, also on PowerLink.

  • 2. Re: Source One users and large OST file not shrinking

    Hello Tim,

    We can use the PSTNullFreeOnClose registry key. However time it takes Outlook to shutdown and if Outlook is forced closed during the compaction process the data file could become corrupt. If you use both this key and the option to empty deleted items on exit, Outlook will take much longer to exit.

    However, this setting can be useful to security conscious users as compacting removes all traces of deleted messages, making it impossible to recover the mail.

    If you want to force Outlook to return this free space every time that you close Outlook, you can add PSTNullFreeOnClose to the registry.  (Replace xx.0 in the path with your version of Outlook.)

    Value Name: PSTNullFreeOnClose
    Value Data: DWORD  1 = compact on close, 0 = don’t compact


    Copy paste the text in notepad and save it as .reg and run to make required changes as per your outlook version.

    Outlook 2003




    Outlook 2007





    Outlook 2010






    Ajay Chanana

  • 3. Re: Source One users and large OST file not shrinking

    Use Shrink OST Tool and easily shrinking your large OST file with third party tool.