What to do if cannot start Microsoft Outlook OST cannot be Accessed error

MS Outlook comes with a user-friendly interface and so has increased its user base. But often, users complain that OST cannot be accessed. So we took this task upon us to find methods to help all to resolve this error in this blog.

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Why does the user rely on these OST files? Let us get to know about it.

Why do you use OST File?

Microsoft Outlook is an email application that can save the file in the form of two extensions-.ost and .pst. This OST file provides you the advantage that it is accessible even in the case of limited or less Internet connectivity. You can even work offline in the OST file without having Internet connections. OST format lets you access the essential data in the case of Exchange Server crash or Exchange Server downtime. Hence, Offline OST files can be used as a backup file to restore the data if the Exchange Server becomes inaccessible. So, all these features make OST the most opted choice to save pieces of information.

What to do when you encounter “Microsoft Outlook OST cannot be accessed”?

If you encounter an error message mentioning Outlook OST file cannot be opened when you try to open Outlook OST file. Then, you can try to open the OST file by using methods such as – starting the Outlook OST file in Safe Mode, turning off Compatibility Mode, and so on. Still, if nothing works out and the OST file refuses to open, this doesn’t mean that you can’t access the OST file again. There are various factors behind OST file corruption that are mentioned below.

But, often you may encounter Microsoft Outlook OST file that cannot be opened. So, what may have caused this, we have shared it in the next topic.

Read here: Top 3 Cheapest OST to PST Converter

Reasons why OST cannot be accessed?

Here are some of the reasons that you are getting into trouble:

Virus or malware attack: A virus or malware attack is another reason behind the damage to the OST file. Hence, we recommend installing a reliable and trustworthy antivirus program in your system.

Power Failure: OST file corruption can be the cause of sudden power failure when the users are working with the OST file.

Bad sectors present on the hard drive: The presence of bad sectors on the hard drive in the place your OST files are stored could lead you to the inaccessibility of OST files.
Synchronization problem: The synchronization trouble between the OST file and Exchange server may also lead you to many OST errors. Hence, always check for a proper network connection.

Abrupt termination of Outlook: If the Outlook application terminates quickly, then the OST file may corrupt or become inaccessible. Hence, to overcome such an issue, you need to close Outlook once you have completed your tasks.
You have got the reason behind the Cannot start Microsoft Office Outlook 2007. Now the issue is how to overcome this problem. For that, let us get to know about the methods that can rescue you.

DIY Strategies to Troubleshoot “Microsoft OST cannot be accessed” Error:

  • End MS Outlook-related processes from Task Manager

For doing that, follow the given steps:

  1. Firstly, right-click on the taskbar or press Ctrl+Shift+Esc to open Task Manager.
  2. After that, click on the Processes (if you are using Win10 OS, click on the Details tab).
  3. In this step, search for one of the processes such as Communicator, Lync, Outlook, or ucmapi. Once you find any of these processes, just select it and click on End Task.

If still a Microsoft Outlook OST cannot be accessed, then try the next method.

  • Restore with SCANPST.EXE

You can easily fix the OST file cannot be accessed with scanpst.exe. It is an inbuilt Outlook data file repair utility. Usually, it happens that the OST file does not open due to corruption. In such a scenario, utilizing Scanpst can automatically fix OST file corruption.

  1. The first thing is you Locate and Open the Scanpst.exe tool by following the below path:
  2. In Outlook 2016, 2019 if the OST file is not opening, then explore Scanpst.exe in the following path:
    C:\Program Files (x86)\Microsoft Office\root\Office 16For Outlook 2013 users if the OST file is not opening, then find Scanpst.exe can in the following path:
    C:\Program Files (x86)\Microsoft Office\Office 15
  3. In the case of Outlook 2007 if the OST file is not opening, then search Scanpst.exe in the following path:
    C:\Program Files (x86)\Microsoft Office\Office 12
  4. After that, click on the Browse option to select the corrupt OST file, and click the Scan button.
  5. Lastly, click the Repair option to start fixing the issue: OST cannot be opened.

If you did not get results with the above method, then try the following methods for resolving the OST cannot be accessed problem.

  • Disable the option of MS Outlook Cached Exchange Mode.
  1. To disable the Outlook Cached Exchange Mode:
  2. Begin by closing the MS Outlook application
  3. After that, go to the Control Panel, and choose Mail.
  4. Here, you need to click on Email Accounts.
  5. The next step is to go to the Email tab and opt for the email address that shows the warning and click on Change.
  6. Now, uncheck Use Cached Exchange Mode.
  7. The final step is to choose Next, and then Finish the task.

If this method wasn’t able to resolve cannot start Microsoft Office Outlook 2007, then try the next method.

  • Terminate Outlook add-ins

The add-ins we get with Outlook help us to customize and modify the Outlook experience. But, faulty add-ins can cause trouble. So, apply these steps to disable Outlook add-ins:

  1. You have to start by searching for the shortcut icon for Outlook.
  2. After that, press and hold the CTRL key and double-click the application shortcut.
  3. Now, you need to click ‘Yes’ when a window prompt asks if you want to start the application in Safe Mode.

Read Here:- Best OST to PST Converters

Restrictions we face with the Manual Methods:

Manual Methods require assistance from a technical user. If that is not possible, then you need to learn these methods. So, you can perform them with precision. But, in case you do not have the time and patience to perform these steps, then you can resolve the cannot start Microsoft Outlook OST cannot be accessed with the use of an alternate method.

Get to learn about it next for fixing the problem permanently.

The manual Methods pose limitations due to which users avoid using such methods. If the above methods cannot solve your problem, then there may be some issues with your OST files that occur like corruption issues. Therefore, try OST File Recovery Tool by which you can repair any damaged or corrupted OST file back to its original self. But, these features are not limited to English files, it also repairs non-English files. With this tool, get maximum and accurate data with Outlook Encryption & Compression. Try all these features today with OST File Recovery v7.0.


Due to uncertain causes, many times Outlook OST cannot be accessed by an end-user. So, we have shared manual methods to overcome such issues. But these manual ways come with restrictions of errors. Hence, we recommend you to use the OST File Recovery tool and get back your valuable OST file data.

About The Author:

As a content writer, I specialize in Email Migration, Data Recovery, Email Backup, and File Management. I have been writing professionally for two years now. There is so much information available in this field that I am intrigued by the newer technologies and techniques.

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