Outlook.ost is in use and cannot be accessed!

Microsoft Outlook has become quite widely used. So much so that there are many people who are so used to working with it, they might as well call themselves experts in it. However, some errors are capable to boggle even the minds of these people. In this article we’ll be highlighting one such error and all you need to know about it.

The OST Error

Most people who work with MS Outlook are familiar with the term OST. It stands for Offline Storage Table and files with .ost extension store your mailbox’s contents when you’re working with Outlook in offline mode. This .ost file is saved on your local machine and it holds your mailbox’s contents in the exact format as they are on the Exchange server. As soon as you connect to the MS Outlook server, all messages and information stored in the offline Outlook client (in the .ost file) are merged with your online mailbox. OST files hence play a major role when a user is facing issues like limited network connectivity or server downtime.

From the above explanation you can understand that damage or corruption to the .ost file could mean inability to access your mailbox data. So it is important to fully understand why.ost files get corrupted, what are the after effects of such damage and how to fix the loss. But before that, what is also worth noting are the notifications or error messages which point to some problem with the OST. Here are common error messages you may see in case your .ost file becomes inaccessible:

  • Outlook.ost file is in use and cannot be accessed. Close any application that is using this file
  • Default Outlook profile ost is in use and cannot be accessed
  • Cannot display the folder. Outlook.ost is in use and cannot be accessed
  • OST file is in use by another application

Reasons behind this error

Here are some of the reasons why such errors could crop up:

  • Problems while synchronizing .ost file on local machine with the Exchange server mailbox
  • Slow or unreliable internet connection
  • Attempt by multiple users to access the same.ost file at one time
  • Runtime conflict of some other software with the Outlook application

After knowing how to identify the error and understanding the reasons behind it, the next obvious step is to try and rectify it. For this there are two approaches explained in the next section.

Solving the OST error through common fixes

To overcome a problem the first step is generally to perform some kind of quick fixes. Many a times such quick fixes actually work wonders. Here are some hit-and-trial things you can do:

  • Quit Outlook and restart it
  • Quit Outlook, restart your PC and then restart Outlook
  • Run the MS Outlook inbuilt utility called “OST Integrity Check”. However, this utility is only available in Outlook 2007 and lower versions. Here are the steps to use this utility:

o   Quit MS Outlook

o   Run ScanOST.exe present in the MS Outlook installation folder

o   In the window that opens, provide appropriate Outlook profile name when prompted

o   When asked to choose between “Work Offline” or “Connect”, choose “Connect”

o   Select from options “Scan all folders” or “Choose folder to scan” as per need

o   You could choose to “Repair Errors” if required and then click on “Begin Scan”. (NOT selecting to “Repair Errors” makes the tool only list down required corrections, NOT perform them)

One or the other alternative above is sure to resolve the OST error in question. However, if you’re unable to regain access to your mailbox even after these fixes, that could mean some major damage to the .ost file. In such a case, the best solution would be to convert your .ost file to .pst file. This conversion is also a good option for Outlook versions later than 2007. Try out here Stellar OST to PST Converter tool to repair and convert Outlook OST file to PST.

Solving the OST error by OST to PST conversion

OST to PST conversion safely transfers objects in an OST file into PST format. Such PST can then be imported into Outlook to access the all mailbox data. Stellar Converter for OST is recommended software to perform outlook OST repair. Some key features of this product is the complete conversion of all your mailbox items from .ost file to .pst file and saving of converted mail messages in MSG, EML, RTF, HTML, and PDF formats.

Here are the steps to convert ost to pst using this software:

  • Download, install and run the software over here: 
  • The main software interface shows the options to either ‘Select’ or ‘Find’ the OST file. Locate the particular file and then click ‘Scan Now’ button

select ost file

  • Next, a progress bar will show that the OST to PST conversion process is on. You can stop the process at any moment by clicking the ‘Stop’ button

scanning progress

  • The left-hand side pane of the software window lists all the converted mail items. Select a mail to view it in detail in the adjoining pane
  • Next, select the format in which you want to save individual converted emails

  • The next window shows save progress of the converted files. You can stop the process by clicking the “Stop” button

  • Finally an information bar will show successful conversion message

Rating by MVP:

Reference: https://social.technet.microsoft.com/wiki/contents/articles/43966.microsoft-outlook-stellar-ost-to-pst-converter.aspx


So try to resolve any issues regarding the OST file as soon as possible. Choose a relevant software to convert OST to PST file in order to avoid further corruption.


  1. James R. Mark September 24, 2015
    • admin October 26, 2015
  2. Lennie October 20, 2015
    • admin October 26, 2015
      • Lennie November 5, 2015
        • admin November 6, 2015

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