Recover Emails From an Inaccessible OST File in Outlook 365: Quick Guide

No one can challenge the authority of Microsoft Outlook in the domain of work communication. This email client is so popular that the term ‘work communication’ has become synonymous with Outlook. One of the vital elements of this email client is an Offline Storage Table (OST) file.

The importance of .ost files increases by several folds when the user works in Outlook 365 environment. This file format is entrusted in the task of providing its users with the access to work with their email and other mailbox content even without the internet connectivity. It may be noted that .ost files store a synched copy of the user’s mailbox on their local device, thus offer offline access. The modifications made during this ‘non-connectivity’ period will be synced later with the restoration of internet. This functionality is extremely beneficial for executives who travel frequently or who works in areas where connectivity issues are normal. 

Sometimes these vital .ost files become inaccessible or orphaned due to corruption or any other reason. Other factors that may lead to inaccessible .ost files include any conflict with third-party apps and synchronization problem between an Outlook data file (.ost) and the mailbox server. Not accessing email messages is not only frustrating but also amounts to waste of enough productive hours. IT experts strongly recommend to reduce OST file size limit to diminish the possibility of corruption arising due to an oversized file. Once the file size is compacted, the additional data and metadata get archived, making the OST file smaller as well as stable. This guide will also shed light on how to recover emails from an inaccessible OST file in Outlook 365. Additionally, we will also explore a professional OST to PST converter tool. 

Factors That Lead to an Inaccessible OST File

Now the question arises why does an OST file become inaccessible? Well, multiple factors can lead to an inaccessible OST file. Some of them are listed below:

• Data file corruption: If the Outlook data file (.ost) gets corrupted owing to sudden system shutdown, it may become orphaned or inaccessible. It happens because the data file is unable to synchronize the email data with the server. 
• Synchronization issues: Any issue with the Exchange server like a shutdown because of any hardware failure can hinder connectivity between the server and offline folder. It leads to corruption that may cause an inaccessible OST file.
• An oversized data file (.ost): An Outlook data file exceeding its size limit is one of the most common issues. It is the main reason that leads to an inaccessible or orphaned .ost file.  
• Malware: An interference by antivirus software can also lead to this issue.
• Software issues: Errors arising during the process of Outlook update or migration can lead to the issue of an inaccessible Outlook data file (.ost). In such a scenario, the email client 

How to Recover Emails from an Inaccessible OST File in Outlook 365?

This part of the guide sheds light on proven techniques to recover mailbox data from an inaccessible Outlook data file (.ost). Follow the below methods:

Fix 1: Shutdown Outlook and Related Processes: Sometimes sync issues are solved by simply closing down the app and related processes. It is because many a times any active process in the background prevents the .ost file from getting accessed. Follow the below steps:

Step 1: Close Outlook on your device:

• Press ‘File’> ‘Exit’ or you can also hit on the ‘X’ icon for the same.
• Open the Task Manager by hitting the Ctrl + Shift + Esc keys on the keyboard.
• Discover the email client in the list of processes (if the application is still active).
• Press ‘End Task’ tab to shut down the Outlook.

Step 2: Shutdown Associated Processes:

• Browse the Task Manager by pressing Ctrl + Shift + Esc keys.
• Checkout any active process with ‘Outlook’ in its name, (for instance, ‘Lync’, ‘ucmapi’ or ‘Outlook.exe’).
• Select the process and then press on ‘End Task’ button.

Step 3: Reopen the Application:

• Browse Microsoft Outlook to validate if the issue has been fixed.

Fix 2: Reduce OST File Size Limit: 

The main reason behind corruption issues in the Outlook data file (.ost) is an oversized file size. With time the data and metadata accumulate, causing this issue. By reduce OST file size limit, an Outlook user can reduce the probability of file corruption and ensure better data management. The email client is loaded with built-in compact feature for the same. Even though this process is automatic, but the user can trigger it manually using below steps:

• Explore the File > Account Settings.
• In the Account Settings go to Data Files. 
• Then explore Settings. After this press Advanced. 
• Now hit on the Outlook Data File Settings tab. 
• After this press Compact Now button to reduce OST file size limit.

Fix 3: Restart Outlook in Safe Mode:

If the file is infected with malware, then the user can try exploring Outlook application in the safe mode. The step-by-step guide for this process is listed below:

Step 1: Shutdown the email client and its linked processes.

• Browse the Task Manager (Press the Ctrl + Shift + Esc keys).
• Discover Microsoft Outlook in the list of processes.
• After this hit on the ‘End Task’ tab to shut down the app.

Step 2: Browse Outlook in a Safe Mode:

• Explore the Run dialog box by pressing Windows key + R.
• Type “Outlook.exe /safe” (without the quotation marks) and press Enter.
• The app will start in a safe mode with basic functionality.

Step 3: Try locating the OST file from Outlook:

• Investigate if the application is successful in locating the Outlook data file (.ost). 

Fix 4: Rebuild the OST File: 

In case none of the methods discussed above works then we can try recreating the OST file. Follow the below-mentioned guide:

• Exit the Outlook application.
• Navigate to the OST file location.

• Rename the targeted data file (.ost) with the .bak extension and create its backup. (Rename [email protected] to [email protected]).

• Now re-start the Outlook application. You will discover a new OST file at the default location. Now sync all your mailbox content from the mailbox server.

It may be possible that even after recreation of the .ost file, some mailbox data items go missing. To discover such missing mailbox content, we need to utilize some professional OST to PST converter tool. The user requires to run the software like Stellar Converter for OST on the backup OST file (created before rebuilding the file). Fast and reliable, this tool can efficiently extract all data files from the OST file. Now the user can look for the missing items and save them in a PST file. Now use the Import/ Export wizard to restore the missing items. 

Conclusion:

An .ost file is a crucial element of Microsoft Outlook. But sometimes this vital file becomes inaccessible or orphaned owing to multiple issues. Such issues range from synchronization errors, conflicting add-ins, and oversized data file sizes to many others. We have explored multiple reasons as well as their solutions for this error in the above guide. The user can employ any of the above-discussed solutions for the issue. In case none of the methods discussed above work, the user has to convert an OST file to PST to regain access to mailbox data using a third-party tool. Such an OST to PST converter tool can efficiently convert mailboxes from an inaccessible .ost file. Stellar Converter for OST is a reliable, user-friendly converter tool that is trusted by IT admins. This tool can quickly and efficiently convert mailbox data from inaccessible or orphaned OST files as well as encrypted IMAP OST files to PST files.