In short, MS Outlook often shows errors and is corrupt. Many users also get the most typical MS Outlook problem, which is "OST File Not Recognized by Outlook." OST file corruption usually happens in many situations. Read this complete blog to find out what caused the mistake, what to do about it, and how to fix this situation.


Let's start with the basics: MS Outlook is one of the most common email clients used by many businesses to communicate. Because of its smart and proactive features, Outlook has always been the preferred choice for consumers. MS Outlook can work with Exchange Server and SharePoint Server. When it works with Exchange Server, it creates OST files.


The OST file is an offline folder that lets us work while we're not connected to the internet or when the internet is slow. Later, when the connection to the Exchange server is made, this OST file is automatically updated in the user's Exchange account. But sometimes these OST files might get damaged, which can cause strange messages like "Outlook Can't Read OST File."


When this issue happens, consumers panic since they don't know how to fix it, which could lead to losing data. But first, let's find out what really caused this problem.


Reasons for the OST File Error


  • OST File Corruption: OST files are easy to corrupt, thus they can get corrupted for any number of reasons, such as a virus assault or hitting the file size limit. This is what causes this strange message.
  • OST File Synchronization: If your OST files can't sync with the Exchange server for some reason, Outlook will give you this error.


How to Fix the Outlook Does Not Recognize OST File Error Manually


Method 1: Make a New OST file


You can make the OST file for any email account by following these procedures.


  • Click on the Mail button in the Control Panel.
  • In Mail Setup, click on Show Profiles, pick your profile, and then click on Properties.
  • Select the Exchange account on the E-mail tab, click Change, then check the box next to Use Cached Exchange Mode.
  • Open More Settings. Select Offline Folder File Settings in the Advanced tab.
  • Now click the "Yes" button after choosing the "Disable Offline Use" option.
  • Go to the Offline Folder File Settings and click the OK and Yes buttons.
  • Now check the box that says "Use Cached Exchange Mode."
  • Press OK, then Next, and finally Finish.
  • Shut down the wizard for setting up your account and email.


Method 2: The Inbox Repair Utility


The Inbox Repair Utility is a built-in tool in MS Outlook that can help you figure out what's wrong. Now, use these steps to remedy the "OST file is not recognized by Outlook" error.


  • Start the inbox repair tool.
  • To choose the OST file, click the Browse option.
  • Press the Start button to begin the scanning process.
  • It will make a list of errors after the scan is done. Then click the Repair option.
  • Now, restart Outlook and see if the OST file works.


Method 3: Use Expert Choice to Fix the Error "OST File Not Recognized by Outlook"


If you still can't open the OST file after trying the two techniques above and get the same error notice that Outlook doesn't recognize the OST file, you should contact an expert for help. As we said before, the two solutions above might not work to fix this OST file error. We recommend that you use GainTools OST to PST Converter. This application is just built to convert OST files into PST files, together with all the email information. This tool will also fix your broken OST file in seconds and give you access to all of your critical emails, contacts, calendar, and more. This useful converter works with all versions of Windows and MS Outlook 2024, 2021, 2019, 2016, 2013, 2010, and so on. 


To fix the "OST file not recognized" error, follow these steps:


  • Open the OST to PST Converter and choose the broken OST file by clicking the browse option.
  • Choose the type of scan you want (Standard, Advanced, or Deep) and then click the OK button.
  • After the scan is done, look at the preview.
  • Click the save button after choosing the folder.
  • When you click the save button, the conversion begins.
  • Now, import this PST file that you changed into your Outlook and check your emails.


In conclusion


If your computer screen shows an error message saying that the OST file is not recognized, you now know what to do. File corruption is the most prevalent cause of Outlook errors, and it can happen at any time without your notice. So, it's always a good idea to be very careful with your data files because they include a lot of important information. We have spoken about all the ways (both manual and automated) that we could fix this problem. You can choose any of them.