Outlook error/ Cannot open .ost file. Must connect to Microsoft Exchange.

Question

Windows 10, 32 bit MS 365 Office. Clicking on APP leads to this message. No idea how to access this.

Answer 1

If you are encountering an error stating that you cannot open the .ost file and must connect to Microsoft Exchange, it is likely due to corruption in your offline Outlook Data File (.ost). Here are steps you can take to resolve this issue:

1. Close Outlook.
2. Delete the .ost file:
   • Navigate to the folder where the .ost file is located. This is typically found at:
     • C:\Users\<username>\AppData\Local\Microsoft\Outlook
   • Find the .ost file that is causing the issue and delete it.
3. Restart Outlook:
   • When you restart Outlook, it will automatically create a new .ost file and download your mailbox data from the Exchange Server.

If you continue to experience issues, you may also want to check for synchronization problems or consider using the Inbox Repair tool (Scanpst.exe) to diagnose and repair errors in your .ost file.

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References:

• Errors have been detected in your .ost file in Outlook
• Synchronization problems occur in Outlook and in Outlook Web App

Answer 2

Hi,

I'm really sorry about the problem you're having. The mistake "Can't open .ost file. "Must connect to Microsoft Exchange" is a sign that the Outlook data file is likely damaged.

Simply to understand more. Can I please ask?

Did this problem start right after something happened, like a Windows update, installing software, a system crash, or a change in your network connection (for example, trying to use Outlook from a new location)?

Are you the only one having this problem, or have others in your company said they can't get into Outlook, too? This helps figure out if it's a problem with the computer or the service.

You can also try to fix the problem by using Microsoft’s Inbox Repair Tool (SCANPST) to check and fix your OST file, turning off any bad Outlook add-ins by starting Outlook in safe mode and turning off add-ins one at a time, and fixing your Office installation through Control Panel or Settings using the Online Repair option.

I hope this is useful. Leave a comment if you want to ask something.

Thanks,