Outlook data file OST is in use and cannot be accessed [How to Fix]

A duplicate of the mailboxes that reside on the server is built on the local machine while using Microsoft Exchange with Cached Mode enabled. This duplicate stored inside Offline Storage Table files are the OST extension data files. An issue with the OST files generally occurs such as “OST is in use and cannot be accessed” error message. This error is faced by many OST file users. So, in this blog, we will discuss all the reasons behind this occurrence of error and the various methods to fix it.

OST files enable users to keep working with their mailboxes even though the Exchange connection gets interrupted.  When the server goes online, all modifications in the local mailbox are combined with its copy of the file.

Holding their benefits aside for a minute, there are several popular drawbacks of OST files such as OST manipulation, locking issues, and limiting their transition between systems. Because of these issues, users sometimes face errors such as “the file is in use and can not be accessed.” This means some software or application already uses the OST file that you are trying to use.

Some of the other errors that are similar to this error may occur as shown below

  • outlook 2010 ost file in use and cannot be accessed
  • .ost file in use error outlook 2010, 2007, 2003
  • cannot display the folder the file outlook ost is in use and cannot be accessed
  • ost file is in use by another application
  • default outlook profile.ost is in use and cannot be accessed

Let’s try to figure out, through this post, why this error happens and how users can fix it.

What are the reasons for OST file error Outlook 2010/2013/2016/2019?

Mainly the problem occurs due to the access of the same OST file at a time.

Besides this, there are some common reasons for this error:

  1. Synchronization of the.ost file with the Microsoft Exchange server mailbox.
  2. Due to poor internet connectivity.
  3. Runtime dispute of some other programs with the Outlook application
  4. Many users attempt to access the same OST file at a time.

Now, after this, let’s discuss some of the important methods to fix this OST error.

How to Solve “OST is in use and cannot be accessed” Error in Outlook  2010/2013/2016/2019?

There are many solutions that you can perform by yourself as given below:

Method 1:  Exit MS Outlook And Destroy all processes associated with Outlook

It is the main solution that may be useful in fixing the errors mentioned above. To accomplish the mission follow the step-by-step guide.

  • Initially, safely close or exit your Microsoft Outlook.
  • Make a right-click on the taskbar and choose the “Task Manager”.
  • Now, pick the “Processes” tab.
  • Navigate the “Communicator“, “Lync“, “ucmapi” or “Outlook“. Search for the “End task” button and press it in the end.

Method 2:  Make Cached Exchange Mode Disabled

This is another approach that could help you solve the problem. You only need to disable the cache Exchange Mode in this method by following steps below:

  • Initially, close and exit the MS Outlook.
  • Next, after closing the application, visit the control panel and open it and select “Mail“.
  • Then pick the “Email Accounts” button >>“Email” tab.
  • Next, select the Email-Id and hit on the “Change“.
  • In the end, untick the “Use Cached Exchanged Mode” >> “Next” >> “Finish“.

Method 3: Launch the ScanOST.Exe  Application

This is the last effective method to fix “OST file error outlook 2010”.

  1. Initially, close and exit the MS Outlook.
  2. Now, launch the ScanOST.exe
  3. Then select the Mailbox >> ‘Repair Errors‘ >> ‘Begin Scan’.
  4. Scanning Hierarchy and fixing errors will take a few minutes.

Method 4: Disabling Defective Add-ins

Add-ins are the main reason behind this type of error. So, disabling them will help you in fixing the error. It will open Outlook in safe mode. Follow the below steps:

  1. Search the shortcut icon for Outlook.
  2. Now, hit and hold the CTRL key and double-click on that shortcut icon.
  3. Then, a notification appears asking “if you want to start the application in Safe Mode”, press ‘Yes’.

If still you are not able to fix the error then the last and the exact option is to repair the inaccessible OST files, so that every error related to it gets resolved automatically. The fast method to quickly repair an OST file is the OST Recovery utility. This tool also converts the OST files into PST, DBX, EML, MSG, MBOX, etc. So, use this recommended utility for better outputs.


This blog concludes the reasons behind the OST file error, then the methods to fix the error manually. Resolving the “OST is in use and cannot be accessed” error could be easier if you use the direct method explained above. Hope you get some useful information through reading this guide.

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