Instruction for converting a large OST file


How to convert a large OST file (over 4 GB) into a Microsoft Outlook PST file?


Conversion of a large OST file requires that all the necessary software components be installed on a 64-bit system.

  1. Microsoft Windows 64-bit
  2. Microsoft Outlook 64-bit
  3. Outlook Repair Toolbox 4.0 or newer version

Only in this case will you be able to overcome RAM limitations and convert OST files of virtually any size.

If all these conditions are met, you can proceed to data conversion. Start Outlook Repair Toolbox and do the following:

  1. Select a source OST file on the first page.
  2. On the next step, select the Conversion mode.
  3. Select the data to be converted (emails, contacts, meetings, et cetera).
  4. Specify the destination path or select the target folder for saving converted data.
  5. Select the Save to PST option.

The process of reading an OST file and exporting its data takes some time, and its duration depends on the performance of your computer and the speed of your hard drive.


When Microsoft Outlook is installed with default settings, the 32-bit version is installed. To learn how to install the 64-bit version of Microsoft Outlook, read this article.