[Solved]‌ ‌Outlook‌ ‌OST‌ ‌File‌ ‌Cannot‌ ‌be‌ ‌ Opened‌ ‌in‌ ‌Outlook‌ ‌2016‌

[Solved] Outlook OST File Cannot be Opened in Outlook 2016

[Solved] Outlook OST File Cannot be Opened in Outlook 2016OST file is created when you configure Outlook with Exchange Server or IMAP account. OST file is the replica of the mailbox on the server and allows you to work even when there is no internet connectivity. However, sometimes, when opening the Outlook, you get an error message – ‘Outlook OST file cannot be opened’

In this post, we’ll be discussing the solutions to fix Outlook OST file cannot be opened error.

Some Common Errors of Outlook OST File

There are various other errors that are also related to the OST file. Some of them are: 

  • OST is in use by another application
  • Microsoft Outlook not responding
  • Default Outlook .ost is in use and cannot be accessed
  • Set of folders cannot be displayed

There could be various reasons behind such errors, such as Outlook’s abrupt shutdown, synchronization issue between Exchange Server and cached OST, malware infection, sudden power failure, etc. However, the common cause for such errors is corruption in the OST file. 

Methods to Fix ‘OST File cannot be Opened’ Error

Here are some effective solutions to fix OST file cannot be opened error.

1. Relaunch the Outlook

Sometimes, simply restarting the Outlook helps resolve various issues. To try to fix the Outlook OST error, you can just close the Outlook program and restart it. Follow the below-mentioned steps: 

  • Close the MS Outlook program.
  • Now launch the Task Manager and select the Processes tab.
  • Try to find the Lync, Outlook, Communicator, or UcMapi. If you find any of them, choose them and select End Process
  • Restart your system and check if the error is resolved. 

2. Disable the Cached Exchange Mode in MS Outlook 2016

You can disable the Cached Exchange Mode in your Outlook 2016. It may help fix Outlook OST cannot be opened error. Follow the below steps: 

  • Close the MS Outlook program. 
  • Go to the Control Panel and select the Mail option. 
  • This will open the mail setup window, wherein you need to click on the Email Accounts option.
  • Now, select the Email tab. This will display the Exchange Account on your screen. 
  • Select the email address and click on Change.
  • Next, uncheck the Cached Exchange Mode option.
  • Click Next and then click Finish.

3. Disable the Conflicting Outlook Add-ins

Sometimes, conflicting or faulty add-ins can cause various Outlook errors, including the Outlook OST cannot be opened error. If this is the case, you can disable the add-ins. To disable the add-ins in your Outlook 2016, you need to start it in safe mode. To do so, you can open the Run dialog box, type ‘Outlook/safe’, and then press Enter. Alternatively, you can follow the steps below to open Outlook in safe mode: 

  • Navigate to the shortcut icon of MS Outlook application.
  • Double-click the application shortcut while holding down the CTRL key.
  • You will see a prompt. Click Yes to run the Outlook application in safe mode.

If the error is resolved, it means the add-ins are causing the issue. Now you can enable the add-ins one-by-one and restart the Outlook to find out which one is causing the issue. When found, you can disable the add-in permanently. 


The Outlook OST cannot be opened error may occur due to various reasons, such as faulty add-ins, synchronization issues, damaged or corrupt OST file, etc. However, you can easily fix Outlook OST cannot be opened error by following the methods mentioned in this post. In case the OST file becomes orphaned or inaccessible, you can use a powerful OST to PST converter software, such as Stellar Converter for OST to extract data from the file. The software can convert OST file of any size into PST file which you can easily import into any Outlook account.