OST is Not an Outlook Data File: Resolve the Error

Microsoft Outlook is a trusted email client widely used by businesses and professionals for its seamless communication, data organisation, and offline access capabilities. However, even this reliable application isn’t immune to technical issues. One common problem users encounter is the “OST is not an Outlook Data File” error.

This issue typically appears with an error message such as:

Cannot start Microsoft Outlook. Can’t open the Outlook window. The set of folders cannot be opened. The file C:\Users\owner\AppData\Local\Microsoft\Outlook\Outlook Data File.ost is not an Outlook data file (.ost).

The error indicates that Outlook cannot recognise or access the OST (Offline Storage Table) file, which stores a synchronised copy of your mailbox for offline access. When this file becomes corrupt, inaccessible, or unlinked from your Outlook profile, it can prevent you from opening Outlook or accessing emails, calendars, and contacts.

In this guide, we’ll explore the main causes of this error, manual repair methods, and a professional recovery solution using the Shoviv OST Recovery Tool to restore Outlook access without data loss.

Before attempting recovery, understanding the root causes of this issue can prevent future data corruption. The next section outlines the main reasons why this Outlook error occurs.

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Causes of the Error ‘OST is Not an Outlook Data File’

Several factors can lead to this Outlook issue. Below are the most common causes:

Corruption or damage in the OST file due to abrupt shutdown or power failures.
Synchronisation failures between Outlook and the Exchange/IMAP server.
Oversized OST file exceeding Outlook’s storage limits.
Faulty or misconfigured Outlook profile settings.
Interference from antivirus programs or third-party add-ins.
Moving, deleting, or renaming the OST file from its original directory.
Hard drive errors or bad sectors are causing files to become inaccessible.
Version mismatches or incomplete Outlook updates after migrations.

When this error appears, avoid deleting your Outlook profile immediately. Instead, try safe recovery methods — manual or automated — that can restore access to your data without risking loss.

Manual Methods to Fix ‘OST is Not an Outlook Data File’ Error

Suppose Outlook fails to recognise your OST file. In that case, you can try the following manual solutions before opting for a professional recovery tool:

1. Method: Update Windows and Restart

Go to Settings > Windows Updates and install all pending updates.
Restart your system and open Outlook to check if the issue persists.

2. Method: Repair the Outlook Profile

In Outlook, navigate to File > Account Settings > Account Settings.
Select your email account and click Repair.
Follow the on-screen instructions, then restart Outlook.

3. Method: Create a New Outlook Profile

Open Control Panel > Mail > Show Profiles.
Click Add, set up a New profile, and configure your email account.
Under Always use this profile, select the new one and relaunch Outlook.

5. Method: Disable Cached Exchange Mode

Go to File > Account Settings > Account Settings > Change.
Uncheck Use Cached Exchange Mode, then restart Outlook.

Note: This restricts offline access but may fix sync issues.

6. Method: Recreate or Rebuild the OST File

In Outlook, open File > Account Settings > Data Files, then click Open File Location.
Close Outlook and rename or delete the existing OST file (e.g., old .ost).
Reopen Outlook — a fresh OST file will be automatically created.

7. Method: Use Microsoft Support and Recovery Assistant (SaRA)

Download and install Microsoft Support and Recovery Assistant from Microsoft’s website.
Choose Outlook > Outlook won’t start or other problems.
Follow the guided steps to diagnose and repair Outlook issues.

8. Method: Try SCANPST.exe (Inbox Repair Tool)

Run exe (found in your Outlook installation folder).
Browse to your OST file and start the repair process.

Note: This works for minor corruption only; orphaned OST files won’t be repaired.

Limitations of Manual Methods

While manual techniques can fix minor corruption, they have certain drawbacks:

Risk of data loss if the OST file is deleted or unsynced.
Time-consuming and requires technical expertise.
No guaranteed success for severely corrupted or orphaned OST files.
Inconsistent results across Outlook versions.
Cannot recover permanently deleted or encrypted mailbox data.

To avoid recurring OST corruption, consider converting OST to PST format regularly. PST files are more portable, easier to back up, and can be repaired directly if corruption occurs.

OST is Not an Outlook Data File: Resolve the Error Professionally

If manual fixes fail or your OST file is severely corrupted, the Shoviv OST Recovery Tool offers a reliable and efficient recovery solution. This professional utility restores access to inaccessible, orphaned, or encrypted OST files — without data loss.

Key Features of Shoviv OST Recovery Tool

Converts OST to PST, MSG, EML, and HTML formats.
Enables direct export to Office 365 and Live Exchange Server.
Maintains folder hierarchy, attachments, and metadata integrity.
Supports large OST files without size restrictions.
Provides a preview of mail items before conversion for selective recovery.
Ensures complete mailbox recovery — including emails, contacts, calendars, and tasks.

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Steps to Recover OST Using Shoviv

Install and launch the Shoviv OST Recovery Tool.
Add the corrupt or inaccessible OST files.
Preview mailbox items (emails, contacts, calendar, tasks, etc.).
Choose the PST export option or migrate directly to Office 365/Exchange.
Select the destination folder and click Start Conversion.

After conversion, import the new PST file into Outlook to regain full access to your mailbox data — safely and efficiently.

Conclusion:

The ‘OST is not an Outlook Data File’ error can occur due to synchronisation issues, file corruption, or faulty profiles. While manual repair methods — like rebuilding OSTs or repairing profiles — can resolve minor problems, they aren’t always effective for serious corruption.

For complete and risk-free recovery, using a professional tool like Shoviv OST Recovery Tool is the most dependable option. It not only restores inaccessible OST files but also preserves the integrity of your data, ensuring you never lose access to crucial emails and attachments again. Must try the free demo version of the Shoviv Software.

Frequently Asked Questions

Can I open an OST file directly in Outlook?

No. OST files are linked to specific Outlook profiles. To access them independently, you must first convert them to PST format.

Is Scanpst.exe enough to fix OST errors?

Not always. It can repair minor corruption but fails to recover orphaned or encrypted OST files.

Where is the OST file stored by default?

The default path is:
C:\Users\<username>\AppData\Local\Microsoft\Outlook

How does Shoviv OST Recovery Tool help?

It converts inaccessible or corrupt OST files into PST, EML, MSG, or HTML formats. It allows direct export to Office 365 or Exchange — ensuring complete recovery.