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How to Open an OST File in Outlook

An Outlook OST file is a local offline copy of mailbox data used by supported Exchange and Microsoft 365 accounts. Outlook normally manages the OST automatically through the email profile that created it

If the original Outlook profile and mailbox are still available, you do not normally need to open the OST as a separate data file - Outlook loads it as part of the account. If the profile has been deleted, the mailbox is unavailable or the OST has been copied to another computer, the file generally cannot simply be attached to Outlook like a PST file.

Open OST file in Outlook

This guide explains how to locate and access an OST file in Outlook and what to do when the original profile is no longer available.

Can You Open an OST File Directly in Outlook?

If the original Outlook profile/mailbox still exists: Outlook normally opens and uses the OST automatically.
If the OST is orphaned, copied from another computer, or disconnected from its mailbox: you generally cannot simply attach it as an Outlook Data File in the way you can with a PST.

In that situation, recover the orphaned OST or use the EdbMails OST to PST Converter to scan the file and export readable data to PST.

OST vs PST Opening Behavior

Capability	OST	PST
Created Automatically by Account/Profile	Yes	No
Used as Offline Mailbox Cache	Yes	No
Open via 'Open Outlook Data File'	Generally no	Yes
Portable to Another PC/Profile	Generally no	Yes
Independent of Original Mailbox	Limited	Yes
Suitable as Recovered/Exported Mailbox File	No	Yes

How to Find the OST File Location in Outlook
1. Open File.
2. Select Account Settings.
3. Select Account Settings again.
4. Open the Data Files tab.
5. Select the account/OST.
6. Choose Open File Location.
Common Windows location: C:Users<username>AppDataLocalMicrosoftOutlook
The actual file location can vary depending on the Outlook profile and Windows configuration, so use the steps above to confirm it directly within Outlook if it isn't in the default folder.
- Method 1: Access OST Through the Original Outlook Profile
  If the Exchange or Microsoft 365 mailbox is still configured and working, open Outlook using the original profile. Outlook will automatically use the associated OST file and synchronize mailbox data with the server.
  If Outlook no longer loads the OST correctly, see Outlook synchronization troubleshooting or the OST rebuild guidance.
- Method 2: Export Accessible Mailbox Data to PST
  If Outlook can already access the mailbox associated with the OST, you can use Outlook's export feature to create a PST copy of the accessible mailbox data.
  - Open the Import/Export wizard. In Outlook, click File, then Open & Export, and select Import/Export.
  - Select the export type. Choose Export to a file, click Next, then choose Outlook Data File (.pst) and click Next
  - Choose the folders to export. Select the account or folders you want, including subfolders if needed, and click Next.
  - Save the exported PST file. Choose a destination and click Finish to complete the export.
  - Open the exported PST in Outlook. Use the Import/Export wizard again, choose Import from another program or file, and select the new PST.
    Note: This is a limitation of Outlook's built-in export feature. It cannot solve the case of a truly orphaned OST that Outlook is unable to load

Can You Move an OST File to Another Computer?

An OST is not designed to be transferred and attached to another Outlook profile like a PST. If the original mailbox still exists, configure the account on the new computer and let Outlook create a new OST. If the original mailbox no longer exists and the old OST contains needed data, recover the OST and export that data to PST.

Need to Open an OST Without Outlook?

If you only need to inspect mailbox contents without Microsoft Outlook or the original Exchange profile, use the EdbMails Free OST Viewer.

What If the OST File Is Orphaned?

If the account/profile that created the OST no longer exists, the file cannot normally be attached directly to a new Outlook profile. Recover the offline OST independently and export its mailbox data to PST or another supported destination.

What If Outlook Cannot Open the OST Because It Is Corrupted?

If the server mailbox is still available, Outlook may be able to rebuild the OST by creating a fresh local cache. If important local data is unavailable from the server, or the damaged OST must be recovered independently, use OST recovery.

How to Access an OST After Outlook Profile Deletion

If the original mailbox still exists, configure the account again and allow Outlook to create a fresh OST. If the mailbox no longer exists, recover the old OST separately.

When Should You Use an OST to PST Converter?

The original Outlook profile is gone
The original mailbox is deleted
Exchange or Microsoft 365 is unavailable
The OST is orphaned
Mailbox data must be moved to another PC or profile
Recovered mailbox data needs a portable Outlook data file

In these scenarios, the EdbMails OST to PST Converter can scan the available OST, preview readable mailbox data, and export the required content to PST:

Add the OST
Scan
Preview
Select data
Export to PST if required

For the full walkthrough, see How to Convert OST to PST. EdbMails supports the Outlook and OST versions listed in the current system requirements.

Choose How to Access the OST File

Your goal	Best route	Important limitation
Continue using an active Exchange or Microsoft 365 mailbox	Configure the mailbox in Outlook and allow it to create/synchronize its OST.	Do not try to attach an unrelated old OST to the new profile.
Read an OST without Outlook	Use an OST viewer to scan and preview the file.	Viewing does not create a reusable Outlook data file.
Open orphaned OST data in Outlook	Recover and convert readable data to PST, then open the PST.	Outlook cannot normally attach an orphaned OST as a standalone data file.
Restore data to a live mailbox	Use PST import or a supported direct migration route.	Choose the destination only after validating the recovered data.

Why Outlook Treats OST and PST Differently

An OST is a synchronized cache linked to the account and profile that created it. A PST is a portable Outlook data file designed to be opened independently. Renaming an OST extension to PST does not convert the underlying file or make it portable.

Safe Access Checklist

Identify whether the original mailbox still exists.
Preserve the old OST before recreating a profile or cache.
Work from a copy when corruption or storage damage is suspected.
Preview the required folders before starting an export.
Validate the PST or destination mailbox after recovery.

OST Viewer vs EdbMails OST to PST Converter

Viewer	Converter
Best when you only need to inspect the data.	Best when recovered data must be saved, opened in Outlook or handed over.
Scans and previews supported readable content.	Scans, previews and exports selected recoverable content.
Does not make the source OST independently attachable in Outlook.	Creates a PST that can be opened or imported according to Outlook capabilities.

Frequently Asked Questions

Can I open an OST file directly in Outlook?
Only if the original profile and mailbox are still active - Outlook loads the OST automatically in that case. You can't manually attach or double-click an OST the way you can a PST.
Why can't I attach an OST file like a PST?
An arbitrary or orphaned OST generally cannot be opened or imported as an independent Outlook data file in the same way as a PST. OST files are tied to the profile and mailbox that created them.
Can I open an OST file on another computer?
Not directly. If the original mailbox still exists, set up the account on the new computer and let Outlook create a fresh OST there. See Can You Move an OST File to Another Computer? above
Can I open an orphaned OST file in Outlook?
No, not directly - Outlook needs the original profile/mailbox connection. Recover the orphaned OST independently and export the data to PST instead.
Can I open an OST file without Outlook?
Yes. Use the EdbMails Free OST Viewer to inspect mailbox contents without Microsoft Outlook or the original Exchange profile.
What happens if I delete an OST file?
If the account/profile is still active and connected, Outlook recreates the OST automatically the next time it syncs with the server.
Can Outlook rebuild an OST file?
If the server mailbox is still available, yes - Outlook can rebuild the OST by creating a fresh local cache. See the OST rebuild guidance for the steps.
How do I open an old OST when the original mailbox no longer exists?
Recover the OST independently and export its data to PST using the OST to PST Converter, or preview it first with the Free OST Viewer.

Related OST Resources

EdbMails OST to PST Converter Free OST Viewer - Open OST Without Outlook Recover an Orphaned OST File Repair a Corrupted OST File Recover Deleted OST After Outlook Profile Deletion Restore OST File on New Drive Import an OST File into Outlook Outlook Data File Cannot Be Accessed

For the complete set of OST recovery, conversion and migration guides, visit the OST Recovery Knowledge Base.

In this manual

Introduction OST vs PST Opening Behavior OST File Location Outlook Profile Deletion FAQs

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