The OST File in My Windows Outlook Is Missing

By Todd Bowerman

If you’re unable to open Microsoft Outlook, you’re going to have a rough time of keeping up with your email and calendar. File corruption, changes to the system by other applications, or simple human error can cause you to lose your OST file; without the OST file, Outlook will be unable to communicate with your Exchange server. You can replace the OST file at any time to restore Outlook functionality.

What Is the OST File?

Microsoft Outlook normally relies on your Exchange server to show and update your email messages, calendar and other data. However, it’s possible to tell Outlook to back this data up to an offline file, just in case you need access to this information when away from Exchange. The OST file stores a copy of your Outlook folders and automatically syncs with the Exchange service whenever you regain access. It is not necessary to enable offline Outlook use, but Outlook may have trouble running without the OST file.

Access Your Mail Settings

Fixing the missing OST file isn’t done through Outlook, but through the Windows Control Panel. Close Outlook and open the Control Panel by swiping to the bottom right corner of the screen, clicking “Settings” and choosing “Control Panel.” Open the “Mail” option, click the “E-Mail Accounts” tab and choose your Exchange account. Click the “Change” button to gain access to the options available for that account. If you do not have administrator access to your PC, you may not be able to open this menu or modify its settings.

Disable Offline Use

Once inside the “Change” menu, you’ll be able to modify Outlook’s offline settings. Clear the check box next to “Use Cached Exchange Mode.” Next, click the “More Settings” button and select the “Advanced” tab. Choose “Offline Folder File Settings.” Click “Disable Offline Use” and then confirm your choice on the dialog box that appears. This will clear the old OST file and prepare your system for a new one.

Recreate the OST File

Click “Offline File Folder Settings” again. Click “OK” when prompted and confirm your choice by clicking “Yes” in the box that appears. Re-check the box next to “Use Cached Exchange Mode,” click “OK,” select “Next” and click the “Finish” button. Close the “Account Settings” and “Mail Setup” boxes when you’re finished. Outlook will have created a new OST file that can be recognized the next time you open the application.