Outlook Ost File Is In Used And Cannot Be Accessed Error

Outlook Ost File
Outlook Ost File

Microsoft Outlook is also known as offline storage, an extensively used application. This server stores users’ mailbox pieces such as Contacts, calendars, Emails, and others. But sometimes, a user can’t open Outlook due to such an error. Outlook Ost file is in use and cannot be accessed.

In this situation, you can apply some fixes that resolve the error. So, read the below post to access the outlook file using the methods mentioned below and acknowledge why this fault occurs.  

Outlook OST Meaning

Outlook application accounts use OST data files. Basically, this is an offline folder file of Microsoft Outlook that allows a user to work offline. However, this OST file store a synchronized copy of the user’s mailbox information on their Outlook system.

In simple words, when you are traveling on an airplane or where the internet connection is unavailable, you can still access all data emails, contacts, and earlier installed tasks. Moreover, you can read and create messages, add contact and make appointments. But your messages or emails will not send correspondingly. No new messages you will get until the internet connection is recovered.

Why Does This Error Occur? – Reasons

Suppose you want to share, save and send MS Office files through an application such as MS Word, Excel, PowerPoint, and others, then suddenly this error occurs. The Outlook Ost file is in use and cannot be accessed. This blunder actually specifies that another program presently uses the outlook file.

However, closing that particular program may steadfastness the error. But the other program or process is not obligatory to use the OST file. Subsequently, it could be numerous other causes that can make the error occur.

The fault can be fixed rapidly if you know and understand the technicalities of MS Outlook. However, if you do not know about it, so don’t worry.

Here are some of the most mutual reasons for such a fault.

  • Defective Internet Connection: Sometimes, a slow internet connection can affect the program to work reliably.
  • Discordancy Problem: The error will arise when there is a mismatch between Lynx and Outlook versions.
  • Unauthorized Access: If a user uses the OST file which is not authorized in that result, the error ensues.
  • Outlook Add-Ins: If a user downloads an outlook Add-in on their device, it occasionally interrupts and causes this blunder.
  • File Use by Additional Program: The abovementioned happens when other applications or programs already use the OST or PST file.
  • Dissimilar File Folder: Make sure that Outlook.exe and Lync.exe run from the same file folder; if not used will get a glitch.
  • Multiple Users: If two or more users try to access the file simultaneously, the fault described above occurs.
  • Programs Running in the Background: When the processes like office communicator 2005/2007, LYNC, UCMAPI, etc., run in the precise, the error must occur.

7 Hasty Fixes: Outlook Ost File is in Use & Can’t Be Accessed Error

When you corroborate and detect the reason behind the error, then the next step you have to do is try and tenacity the issue. We have suggested and explained methods to help you fix the evasion. The username of the file OST is in use and cannot be accessed.

Outlook Ost File
Outlook Ost File

1st Method: Start Again your System and Internet Router

Try just a simple step. Shut down your system, close the internet connection, and then start again. Now check if the problem exists or ends.

2nd Method: Close Microsoft Outlook and Linked Programs

If multiple users are using Outlook and some programs connected with Outlook are running in the background may cause the MS Outlook OST file to work properly. Follow these below steps to doggedness to end or close the programs in the background.

  • First, close the Microsoft Outlook application.
  • Then open the task manager by pressing the CTRL + SHIFT + ESC on your system.
  • A sorcerer will appear on the screen; tap on the processes tab here.
  • Now select the applications such as Outlook, Lync, Communicators, or UCMAPI.
  • Then click on the End Task to close the all-selected applications.
  • After that, check whether the Fault resolves or not.

3rd Method: Disable And Then Enable the Cache Exchanged Mode

Suppose both of the above fixes do not help you fix this problem. So, you can try another method to disable the Cached Exchange Mode. However, cache exchange mode permits a user to work while disconnected from the internet in Outlook. Provisionally deactivated, it can sort out the problem.

Track these simple steps to disable the Cached Exchange Mode.

  • Close the Microsoft Outlook applications
  • Then open the control panel. Here tap on the Mail option.
  • Now select the Email Accounts to tab from the popup window.
  • Select the change option from the email connected to your outlook account.
  • Then disable the Use Cached Exchanged Mode option.
  • After that, select Next and then select the Finish option.
  • Now turn on the Cached Mode.

4th Method: Repair Outlook OST File with Scan OST.exe Application

Users have another method to apply MicrosoftOutlook: the inbuilt data file inbox has a repair tool, Scan OST.exe. Though this tool is unavailable in MSOutlook 2010 and later series, Microsoft provided Scan to fix the issues earlier.

Moreover, 2010 Outlook and later series have Scanpst.exe tools to repair the file. Correspondingly this tool can repair both OST and PST files. So, let us hover over to use this efficacy by following the below steps.  

  • First, close the Microsoft Outlook application on your system.
  • Then open Scanost.exe or Scanpst.exe and browse the location of the Outlook OST file installed on your system that we share in the below table.
  • Select the Mailbox, then select the Repair Errors option.
  • Then click on the Begin Scan option for scanning.
  • It will take a while to scan and then fix errors. That’s it.

Outlook OST File Location (Different Versions)

Outlook 2007 (32bit)

Outlook: C:\Program Files\Microsoft Office\Office12

Outlook 2007 (64bit)

Outlook: C: Program Files (x86) \Microsoft Office\Office12

Outlook 2010 (32bit)

Outlook: C:\Program Files (x86) \Microsoft Office\Office 14\

Outlook 2010 (64bit)

Outlook: C:\Program Files\Microsoft Office\Office 14\

Outlook 2013 (32bit)

Outlook: C:\Program Files (x86) \ Microsoft Office\Office15\

Outlook 2013 (64bit)

Outlook: C:\Program Files\Microsoft Office\Office15\

Outlook 2016 (32bit)

Outlook: C:\ Program Files (x86) \Microsoft Office\Office16\

Outlook 2016 (64bit)

Outlook: C:\Program Files\Microsoft Office\Office16\

Outlook 2019 (32bit)

Outlook: C:\Program Files(x86) \Microsoft Office\root\Office16\

Outlook 2019 (64bit)

Outlook: C:\Programs Files\Microsoft Office\root\Office16\

5th Method: Discover and Turn Off Sticky Outlook Add-Ins

As we all know, Add-ins actually increase the Outlooks function system. But sometimes defective add-ins can cause issues. Like, for creating the OST files unreachable for users. Therefore, turning off these faulty add-ins can fix the error, and a user can straightforwardly access the outlook account and OST file.

Firstly, you have to discover if the fault occurs due to the result of the add-in. To find it start the Outlook app in Safe Mode. To do that, track these simple steps.

  • Exit the Microsoft Outlook. Then press Windows+R tabs at a time.
  • Now type Outlook/Safe and then tap on the enter button.
  • After that, use Outlook normally and check whether the fault is fixed.

NOTE: When the issue is resolved, run Outlook in default mode, turn off the add-ins, and look for any errors. Doing so may help ensure that your system has undefeated add-ins and that the problematic add-ins are removed.

6th Method: Recreate the OST File

Another option for the users is to try to rename the file. Most probably, it will sort out the error.

  • Exit the Outlook app and then hover over the OST file.
  • Change the name of the OST file extension to .bak extension.
  • Now navigate to Outlook. Doing that will change the OST file name and synchronize the mailbox items.

7th Method: Convert OST File Data into Reliable File Format

if the error is still present and the file is not accessible; users have another method: renovate the OST file. This method will help in repairing little faults within the OST file.

However, to change the file format of the Ost file, there are two different methods that you can apply. Below we describe how you can convert the OST file into PST file format.

(i)            Renovate the Ost into PST file VIA Import/Export Feature of Outlook

  • At first, hover over the Microsoft Outlook Application.
  • Open the file, and here selects the Open & Export option.
  • Then select the Import and Export option. Then click on export to a file.
  • Now tap on the Next tab, and choose the folder from which items you want to import.
  • Then locate the destination folder to save the PST file.
  • After that, click on the Finish tab to confirm it.

(ii)           Convert the OST File Via Third Party Tool

Convert the OST File Via Third Party Tool
Convert the OST File Via Third Party Tool

One of the most capable methods of converting the OST file into a PST file is using a third-party tool. https://www.stellarinfo.com/convert-ost-to-pst.php That can help the user resolve the OST errors successfully and make it approachable.

The tool we mentioned here faultlessly resolves all the OST file issues that use its integrated algorithms and recovers the OST data. Moreover, the user can easily recover and change the file format without installing the application tool. However, the tool converting PST files is easy to use and can be moved to another system. the tool correspondingly offers a free trial version on its website.


Microsoft Outlook is an excellent application with all the necessary features and enhances your business organization. However, no application is free of troubles or issues ( minor or major)- the same in the case of OST files. One such commonly occurring problem is “OST file is in use and cannot be accessed”. Thus, in order to use the Microsoft Outlook application in a normal regular way, it is important to eliminate any corruption and errors.