Outlook OST cannot be accessed, You must connect to Microsoft Exchange

Some Office users are unable to access Outlook on their computer. When trying to do the same, the following error message pops up out of nowhere and they want to know how to resolve it.

Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The file <filename>.ost cannot be accessed. You must connect to Microsoft Exchange at least once before you can use your Outlook data file (.ost).

Let us try to troubleshoot this issue with some simple solutions.

Outlook OST cannot be accessed, You must connect to Microsoft Exchange

If you see The file .ost cannot be accessed, You must connect to Microsoft Exchange in Outlook, try the following solutions.

1. Edit Registry
2. Remove Outlook Credentials
3. Use Inbox Repair Tool
4. Repair Outlook

Let us talk about them in detail.

1] Edit Registry

Once the user changes the password of their Microsoft account, Outlook asks them to connect to the Microsoft Exchange to access the data file of Outlook and it doesn’t display the window where you need to type the password. To resolve this issue, we need to force Outlook to show the window where one needs to write the account name and password. To do the same, launch Registry Editor from the Start Menu or by Win + R, type “Regedit” and hit Enter.

Once the Registry Editor window is launched, go to the following location.

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity

Look for EnableADAL from the left panel. If you are not able to find the value, right-click on the empty space, and select New > DWORD (32-bit) Value. Rename the newly created value to EnableADAL. Now, double-click on it and set the Value Data to 0.

Now, look for DisableADALatopWAMOverride, if you can’t find it, create a new value and name it DisableADALatopWAMOverride. Set the Value Data of this value to 1.

Close the Registry Editor and restart your computer. Launch Outlook and see if it worked.

2] Remove Outlook Credentials

Next up, we should try to remove your credentials using Windows Credential Manager and then add them again to see if that help. To do the same, launch Credential Manager from the Start Menu and the credentials of Outlook. Once the credentials are removed, launch Outlook and sign in again. To remove your credentials, follow the prescribed steps.

1. Launch Credential Manager from the Start Menu.
2. Look for Outlook credentials, it will have the keyword Outlook.
3. Expand it and click on the Remove button.

Once done, launch Outlook, and sign in. Hopefully, this will do the job for you.

Read: The file username ost is in use and cannot be accessed Outlook error

3] Use Inbox Repair Tool

Repair Outlook OST personal data files and see if it helps. Inbox Repair Tool can recover items from an offline folder or .ost files. The OST Integrity Check Tool will help you fix corrupted .ost files.

4] Repair Outlook

You may also see the error code in question if the Outlook app on your computer is corrupted. One of the ways is to repair Outlook using Windows Settings. Follow the prescribed steps to do the same.

1. Launch Settings by Win + I.
2. Go to Apps > Apps & Features.
3. Search for Outlook.
   • For Windows 10: Click on the app and select Advanced Options.
   • For Windows 11: Click on the three vertical dots associated with Outlook and click on Advanced Options.
4. Finally, click on Repair.

This may take some time but will resolve the issue for you.

Hopefully, you are able to resolve the issue using the solutions mentioned in this article.

Also read: Email in Outlook not syncing in Windows; Repair Outlook account 

Why is my Outlook not connecting to the Exchange Server?

Your Outlook may not be able to connect to the Exchange Server if your bandwidth is low. You can try checking the same using a free Internet Speed tester. In case, the Internet is not the cause, there might be something wrong with your profile. We would recommend you check this post on what to do when the connection to Microsoft Exchange Server is unavailable. Hopefully, you will be able to resolve the issue easily.

How do I connect my Microsoft Exchange account?

To connect to your client Microsoft Exchange account, ask the administrator to first enable the feature from the Manage application > Extension tab. Once that’s done, follow the prescribed steps to connect to Microsoft Exchange account.

1. Go to Settings > Extension.
2. Look for the Microsoft Exchange extension and click Connect.
3. Select the Authentication Method and follow the on-screen instructions to connect to your account.

That’s it!

Read Next: Fix Outlook not connecting to Server on Windows.