How To Fix Oversized OST Errors With An Advanced Strategy

OST files contains the important data files of Exchange Mailbox, it contains replica of data items that are stored in exchange server.However, there is a predefined size limit on Exchange offline OST files. the ANSI OST file has 2 GB space whereas UNICODE OST has 20 GB to 50 GB available space. If the user will stuff more data than it’s predefined space in OST file, it will causes corruption in OST file.

However, sometimes for freeing up some space, if the user is trying to delete the few emails, then there will be no effect on the volume of data stored in OST file as the deleted items are also get stored in Deleted item folder.Whenever, OST file reaches to it’s maximum limit, system will start showing problem and errors. However, there also exist solution for this problems, In this article we will discuss the issues or error caused due to over sizing of OST files and it’s solution.

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Fix OST File Errors

  • To fix the issue of oversized OST file, one can increase the UNICODE registry values to increase OST file size limit:
  • With MaxLargeFileSize entry, user can determine the maximum size that OST files can expand to. and
  • with WarnLargeFileSize registry entry, one can determines the maximum data OST can have. User can go for the following procedure for increasing the values of OST file with UNICODE Registry values.

Method For Dealing Oversized ANSI OST File

Microsoft has a tool namely OST Crop tool that truncates the overall file volume. However, there is some data loss in resultant OST files.

Other Tips To Optimize OST File Size

  • User must delete the unwanted mailbox items from different folders
  • Must Empty the Deleted Items folder.
  • User must perform the Compact OST file operation


When the size of OST file exceeds it's limit, user can not add any data in it or perform any action. when user try to perform any action, it will start showing errors. There are many manual as well as commercial methods available to tackle this issue. When talking about manual procedures there are option like compacting, increasing registry values and cropping tools are available to increase size limit of OST file. However, user can also use Import OST Files application which is a third party tool to tackle this issue and.