OST Is Not an Offline Folder File: 3 Fixes for This Outlook Error
The “OST is not an offline folder file” error in Outlook means the OST file is corrupt or was created by a different Outlook profile. You can fix it by deleting the OST and letting Outlook recreate it, or by repairing the OST file with a dedicated repair tool to recover emails before recreating.
You open Outlook and get this message:
“Cannot open your default email folders. The file [path].ost is not an offline folder file.”
This is one of the most common Outlook errors. It means Outlook cannot read the local OST cache file. This guide covers what causes it and how to fix the OST is not an offline folder file error in three steps.
What Causes This Error?
The “OST is not an offline folder file” error appears when:
- The OST file is corrupt. Power cuts, crashes or antivirus interference can damage the OST file structure.
- Wrong OST file. The OST is associated with a different Outlook profile or Exchange account. If you reinstall Outlook or change your profile, Outlook may point to the old OST file.
- OST created by a different version of Outlook. Opening an OST from Outlook 2010 in Outlook 2019 can cause this error in some cases.
- File system errors. Disk errors can corrupt the OST header, which Outlook reads first to validate the file.
Fix 1: Delete and Recreate the OST File
This is the quickest fix if the OST error is caused by a corrupt file and your emails are still on the Exchange server.
- Close Outlook completely.
- Navigate to the OST file location. The default location on Windows 10 and 11 is:
C:Users[Username]AppDataLocalMicrosoftOutlook - Find the .ost file. It is usually named after your email account (e.g., user@company.com.ost).
- Rename the file by adding .old to the end (e.g., user@company.com.ost.old). Do not delete it yet in case you need to recover data from it.
- Open Outlook. It will create a new OST file and re-sync your mailbox from the Exchange server.
This fix only works if the emails still exist on your Exchange server. If you have emails that are only in the local OST and not on the server, use Fix 2 first to recover them.
Fix 2: Repair the OST File
Microsoft’s built-in scanpst.exe (Inbox Repair Tool) does not repair OST files. For OST repair, you need a dedicated OST repair tool.
The Turgs OST Repair Wizard scans the corrupt OST file, recovers all readable email data and exports it to PST format so you can import it into Outlook.
Fix 3: Create a New Outlook Profile
If the OST error is caused by the wrong OST being associated with your profile, creating a new Outlook profile fixes it.
- Open the Windows Control Panel and search for Mail.
- Click Show Profiles.
- Click Add to create a new profile. Give it a name and click OK.
- Configure your email account in the new profile.
- Set the new profile as the default by selecting Always use this profile.
- Open Outlook. It will create a new OST and sync from the Exchange server.
How to Find Your OST File Location
If you cannot find the OST file manually:
- Open Outlook and go to File then Account Settings then Account Settings.
- Click the Data Files tab.
- Select your Exchange account and click Open File Location.
This opens the folder containing the OST file directly.
If you need to convert the recovered OST data to MSG format, see the guide on converting OST to MSG. For PST-related errors, the find Outlook PST password guide covers password recovery for locked PST files.
Did the error appear after a Windows update, a PC crash or after reinstalling Outlook?
Frequently Asked Questions
Can I just delete the OST file to fix the error?
Yes, if your emails are all on the Exchange server. Delete or rename the OST file, then open Outlook and it creates a fresh one. If you have any emails that exist only locally (not on the server), back them up first using an OST repair tool.
Why does Outlook keep creating a corrupt OST?
If Outlook corrupts the OST repeatedly, the issue is usually an antivirus program scanning the OST file while Outlook is writing to it, or a failing hard drive. Add the OST file location to your antivirus exclusion list and run CHKDSK on the drive.
Is the OST the same as the PST file?
No. OST is the offline cache of an Exchange or IMAP mailbox. PST is a standalone email archive file. OST is tied to an account; PST is portable and independent.
Can scanpst.exe repair an OST file?
No. Microsoft’s scanpst.exe only repairs PST files. For OST repair, use a dedicated OST repair tool or simply delete and recreate the OST if your emails are on the server.
What if Outlook creates a new OST but the error returns?
Check if there are multiple .ost files in the Outlook folder for the same account. Delete all old ones. Also verify your Exchange connection is working and your mailbox is accessible from OWA (Outlook Web App).
Can I open an OST file without Outlook?
Not natively. But an OST conversion tool can extract the email data from the OST file and export it to PST, EML or other formats that you can then open in Outlook or other email clients.
