Fix Office 365 OST File Cannot Be Opened Issue

Summary: Are you facing Office 365 OST file cannot be opened error. If, yes then in this article, we are going to discuss manual ways to fix this issue. Also, In case if your Office 365 OST file is not accessible then taking the help of OST to PST Converter tool is the best way to resolve this issue.

Microsoft Outlook is an email application that gives different facilities to the clients. In Outlook, the OST file is used so as to do the everyday assignments. Not at all like the PST file, one needs not local machine continually interfacing with Server as it permits to work offline and adjust with Microsoft Exchange Server to update the changes.

The Outlook OST data file gets damaged simply like some other file. It faces corruption because of different viruses, malware, and different issues. Because of the corruption, OST file mailbox data items including messages, contacts, calendars, events, journals, and so on become difficult to reach to the clients. In such situations, numerous problems spring up like ‘Office 365 OST file cannot be opened’. One approach to spare messages and to prevent any such activity is to backup messages at an ordinary interval, archive Outlook OST file to read email messages.

Important Note: In case if you are Office 365 OST file cannot be opened issue, then the user can take the help of SysTools OST Converter. This allows the user to open, access, and export the OST data to Outlook PST format. After saving the data in PST format the user can easily.

A Few Reasons For Getting “Office 365 OST Cannot Be Opened”

There are some likely reasons which may cause a previously mentioned error and are filed underneath:

  • Unexpected termination of Outlook when OST file is being used
  • Inappropriate establishment of Outlook
  • Bringing in OST files in an inappropriate way
  • Interference while sharing OST file over the system
  • Synchronization error between the OST file and Exchange Server mailbox items
  • Leaving a communicate gathering or connection

Manual Strategies to Fix Office 365 OST Cannot be Opened Error

Clients can figure this OST file issue utilizing manual methodologies. For this, first, take the backup of the OST file. On the off chance that the issue proceeds, you can attempt to restart the framework. Here, the manual strategies for fixing “OST file cannot be opened” error:

Strategy 1: End whole Outlook related procedures


  1. Close MS Outlook
  2. Right-click on the Taskbar menu and afterward click on Task Manager .
  3. Go to the Processes
  4. Presently, in the Processes tab, search for the procedures Communicator, Lync, Outlook, or Ucmapi.
  5. On the off chance that any of these procedures found, select, and click on the End Process.

Strategy 2: Disable Outlook Cached Exchange Mode


  1. Close MS Outlook and go to the control panel.
  2. Into the Control Panel, click on Mail choice, and afterward select Email Accounts.
  3. Under the Email Accounts, hit a tick on the Email
  4. Presently click on Exchange file and afterward on Change.
  5. Uncheck the Use Cached Exchange Mode option under offline settings and hit Next to complete the procedure.

As we have discussed the manual strategies to fix the error but the manual strategies are extremely long, repetitive, and tedious. It is a lumbering undertaking for non-specialized clients as it requires some specialized data. Moreover, it does not guarantee data honesty and security.

Automated Method to Fix Office 365 OST File Cannot Be Opened Error

If the above strategies don’t work to fix the “Office 365 OST cannot be opened” error, you can choose ScanPST.exe utility to fix this error. Although, ScanPST.exe works just if there should arise an occurrence of minor OST file error. Consequently, it is constantly prescribed to utilize a third-party tool such as SysTools OST Converter tool to recover and change over highly damaged OST files and the data related to it into PST file format. By using this application the user can easily open and access the OST file and allows the user to export in PST format.

Follow the mentioned steps to Open and Access Office 365 OST files 

  1. Install and Run the OST Converter Application.

2. Click on add file and Select the OST File from your system.

3. Now choose the Scan mode from Quick and Advanced Scan.

4. Click on the Export button and select the desired PST format, after that browse the destination location to save the resultant OST file data.

Also Read: The user can also read this post to Import OST to Office 365 Application.


However, utilizing the above manual techniques, one can without much of a stretch determination “Office 365 OST file cannot be opened” error. However, if the difficult despite everything happens, you can without a doubt go for a fast and better solution, you can decide to use SysTools OST converter.


About Jackson Andrew

I am SQL Server database administrator having 9+ years of Experience in SQL Database management. I love to share my knowledge of SQL server related problems.

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