How can I open an orphaned OST file without Exchange Server?

Download Univik OST Viewer (free), install it on Windows, click 'Add OST File', and select your orphaned .ost file. The viewer opens OST files independently without needing Exchange Server connection, Outlook profile, or the original email account. This works even after leaving an organization or account deletion.

What is an orphaned OST file and why can't Outlook open it?

An orphaned OST file is an Outlook Offline Storage Table file that has lost its connection to the original Exchange mailbox. This happens when you leave an organization, your Exchange account is deleted, or the server becomes unavailable. Microsoft Outlook requires an active Exchange connection to open OST files, making orphaned OST files inaccessible through normal means.

Can I access my work emails after leaving a company using OST Viewer?

Yes, if you have a copy of your OST file from your work computer, OST Viewer can open it and display all emails, contacts, calendar items, and attachments even after your Exchange account has been deactivated. The OST file contains a complete offline copy of your mailbox.

What's the difference between OST and PST files?

PST (Personal Storage Table) files are independent data files you can open anytime. OST (Offline Storage Table) files are synchronized copies of Exchange mailboxes designed to work only when connected to the original Exchange account. When that connection is lost, OST files become 'orphaned' and inaccessible to Outlook, but OST Viewer can still open them.

Does OST Viewer work with Office 365 and Microsoft 365 OST files?

Yes, Univik OST Viewer fully supports OST files created by Office 365, Microsoft 365, Exchange Online, and all versions of Outlook from 2007 to 2021. It can open OST files regardless of whether the Microsoft 365 subscription is still active.

Opens Orphaned OST Files, No Exchange Required

Univik OST File Viewer
Access Emails after Exchange Disconnection

Open orphaned, inaccessible and disconnected OST files without Microsoft Outlook or Exchange Server connection. Recover access to your emails after leaving an organization, account deletion or server unavailability.

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Version 5.8 | 22 MB | Windows 7/8/10/11 | No Exchange needed

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Common OST Problems

When OST files Become Inaccessible

These situations make Outlook refuse to open your OST file, but OST Viewer can help.

Left Your Job

You quit or were let go. Your company deactivated your Exchange account, but you copied your OST file before leaving. Outlook now refuses to open it.

✓ OST Viewer: Opens your OST file instantly. No Exchange account needed. Access all your work emails.

Office 365 Subscription Expired

Your Microsoft 365 subscription ended or wasn't renewed. Your OST file remains but Outlook can't connect to sync it.

✓ OST Viewer: Works offline. View all your emails without any active subscription.

Exchange Server Decommissioned

Your organization migrated to a new system or cloud platform. The old Exchange server is gone, making OST files orphaned.

✓ OST Viewer: Access archived emails from the old server without any infrastructure.

Outlook Profile Deleted or Corrupted

You reinstalled Windows, created a new Outlook profile or the old profile got corrupted. Outlook won't recognize the existing OST file.

✓ OST Viewer: No profile needed. Opens OST files directly without Outlook configuration.

OST Recovered from Old Computer

You found OST files on an old hard drive, backup or from a deceased family member's computer. No way to connect to the original account.

✓ OST Viewer: Opens any OST file from any source. No original account required.

Legal Discovery or Forensics

You received OST files as evidence for litigation or investigation. You need to view contents without connecting to any server.

✓ OST Viewer: Read-only forensic viewing. Never modifies original evidence files.

Quick Summary, What is OST Viewer?

Univik OST Viewer is a free Windows application specifically designed to open orphaned, inaccessible, and disconnected Outlook OST (Offline Storage Table) files without requiring Microsoft Outlook, Exchange Server connection, or the original email account.

The OST problem: Unlike PST files which are portable, OST files are tied to a specific Exchange mailbox. When that connection breaks (job change, account deletion, server migration), Outlook refuses to open the OST file, even though all your emails are still inside it.

How OST Viewer helps: It bypasses Outlook's Exchange requirement and reads OST files directly. You can view all emails, contacts, calendar appointments, tasks, and attachments exactly as they were when you last synced.

Technical details: Supports OST files from Outlook 2007, 2010, 2013, 2016, 2019, 2021, Office 365, and Microsoft 365. Works with encrypted OST files (if you have the password). Handles files up to 50GB+. Operates in strict read-only mode.

Common use cases: Accessing work emails after leaving a company, recovering emails when Office 365 subscription expires, viewing OST files from old computers or backups, forensic examination of email evidence.

OST Viewer Facts

✓ 100% Free
✓ Opens Orphaned OST
✓ No Exchange Needed
✓ No Outlook Required
✓ Encrypted File Support
✓ Read-Only (Safe)
✓ Office 365 OST Support
✓ Works Offline

Understanding OST Files

OST vs PST: What's the Difference?

Understanding why OST files behave differently helps explain why you need a specialized viewer.

OST FILE

Offline Storage Table

A synchronized copy of your Exchange/Office 365 mailbox

⚡ Created by: Outlook when connected to Exchange
⚡ Purpose: Offline access to emails
⚡ Tied to: Specific Exchange account
✗ Portable: No, won't open without original account
✗ Outlook behavior: Refuses to open orphaned OST

The problem: When Exchange connection is lost, your OST file becomes "orphaned" and Outlook won't open it.

≠

PST FILE

Personal Storage Table

An independent, portable data file you control

⚡ Created by: User export or Outlook archiving
⚡ Purpose: Backup, archive, transfer
⚡ Tied to: Nothing, fully independent
✓ Portable: Yes, opens on any computer
✓ Outlook behavior: Opens without issues

No problem: PST files work independently. Use our PST Viewer if needed.

How Exchange - OST Synchronization Works

✓ Normal Operation (Connected)

Exchange Server

Outlook

OST File

Emails sync between server and OST file

✗ Orphaned State (Disconnected)

No Access

Blocked

OST File

ORPHANED

OST file is intact but Outlook won't open it

OST Viewer Solution: Bypasses the Outlook Exchange requirement and reads OST files directly, no server connection needed.

Powerful Features

What OST Viewer Can Do

Every feature is designed to help you access orphaned OST files.

Open Orphaned OST files

The core capability, opens OST files that have lost their Exchange connection, without requiring any server access or Outlook profile.

Encrypted OST Support

Opens encrypted OST files when you provide the correct credentials. Supports Microsoft's encryption used in Office 365 and Exchange Online.

Complete Mailbox View

See everything: Inbox, Sent Items, Drafts, Deleted Items, Calendar, Contacts, Tasks, Notes, the full folder structure as it was in Outlook.

Attachment Recovery

Preview attachments directly in the viewer. Save individual files or batch-save all attachments from selected emails to your computer.

Advanced Search

Find specific emails by sender, recipient, subject, date range or keywords. Search across all folders or within selected folders only.

Full Email Rendering

View emails exactly as they appeared in Outlook, complete HTML formatting, inline images, tables, and styled text preserved.

Office 365 OST Support

Fully compatible with OST files created by Microsoft 365, Office 365, Exchange Online, and all modern Outlook versions (2007-2021).

Works 100% Offline

No internet connection required after installation. Your OST data never leaves your computer, perfect for sensitive or confidential emails.

Read-Only Safety

OST Viewer never modifies original files. Guaranteed data integrity makes it suitable for forensic analysis and legal discovery.

The Technical Problem

Why Outlook Can't Open Your OST File

Understanding Microsoft's design decision helps explain why you need a dedicated viewer.

Microsoft's OST Design Philosophy

Microsoft designed OST files as temporary synchronized caches, not as portable data stores. Here's what this means:

What Outlook Thinks

OST is just a local cache of server data
If server is gone, OST is "stale" and useless
User should access data from server, not OST
Opening orphaned OST could cause sync conflicts
Better to block access than risk data corruption

What You Actually Need

Your emails are still inside the OST file
Server access is no longer possible
You just want to read old emails
You don't need to sync, just view
The data has personal/business value

OST Viewer bridges this gap. It ignores Outlook's Exchange verification and reads OST files directly, giving you read-only access to emails Microsoft has locked away.

Download OST Viewer →

Quick Start Guide

How to Open Orphaned OST files

Access your emails in 5 simple steps.

Step 1: Locate Your OST File

Find your OST file on your computer. Default locations:

Windows 10/11: C:\Users\[Username]\AppData\Local\Microsoft\Outlook\
Office 365: Same location, file named [email]@domain.com.ost

Tip: If you're recovering from another computer, copy the OST file to your current machine first.

Step 2: Download OST Viewer

Get the free installer from our website. Only 22 MB download.

Download OST Viewer →

Step 3: Install and Launch

Run the installer and follow the setup wizard. No special configuration needed. Launch OST Viewer after installation.

Step 4: Add Your OST File

Click "Add OST File" in the toolbar. Browse to your orphaned OST file and select it. If the file is encrypted, enter your credentials when prompted.

Step 5: Browse and Recover

Navigate through folders just like in Outlook. Click emails to preview. View attachments, search for specific messages and print or save what you need.

⚠️ Important: OST Viewer is for viewing orphaned OST files. If you need to convert OST to PST or other formats, check out our OST Converter tool.

Real Stories

How Users Recovered their Emails

These people were in the same situation as you. Here's how OST Viewer helped them.

"After I left my company, I realized I had 5 years of important project emails stuck in an OST file. Outlook refused to open it without Exchange. OST Viewer saved me, I found every email I needed."

Michael K.

Software Engineer, Former Microsoft Employee

"My father passed away and I needed to access his work emails for estate matters. His company had deleted his Exchange account. OST Viewer let me open his laptop's OST file and find everything we needed."

Sarah L.

Estate Executor

"We migrated from on-premise Exchange to Microsoft 365. Some users had 10+ years of emails in old OST files that didn't migrate properly. OST Viewer helped us recover and review everything."

James R.

IT Director, Healthcare Organization

"For eDiscovery in a lawsuit, we received several OST files as evidence. We couldn't connect them to any Exchange server. OST Viewer let us examine all emails without any infrastructure setup."

Patricia N.

Legal Analyst, Law Firm

"Our Office 365 subscription lapsed for 3 months. When we renewed, half our mailboxes were gone. Thankfully, OST files on user machines still had everything. OST Viewer was our lifesaver."

David T.

Small Business Owner

"I found my old laptop from 2015 with an OST file from my previous employer. Just out of curiosity, I tried OST Viewer, and found old photos and documents I thought were lost forever."

Amanda T.

Marketing Manager

Technical Details

System Requirements & OST Compatibility

System Requirements

OS	Windows 7, 8, 8.1, 10, 11
Architecture	32-bit and 64-bit
RAM	4 GB minimum (8 GB recommended)
Disk Space	150 MB for installation
.NET Framework	4.5 or higher
Outlook Required?	No
Exchange Required?	No

Supported OST Versions

Outlook 2007	✓ Supported
Outlook 2010	✓ Supported
Outlook 2013	✓ Supported
Outlook 2016	✓ Supported
Outlook 2019	✓ Supported
Outlook 2021	✓ Supported
Office 365 / M365	✓ Supported

Additional OST Compatibility Notes

✓ Orphaned OST files

✓ Encrypted OST files

✓ Compressed OST files

✓ Exchange Online OST

✓ Exchange Server OST

✓ IMAP OST files

✓ Large OST (50GB+)

✓ Unicode OST format

✓ Cached Exchange Mode OST

Common Questions

OST Viewer FAQs

To open an orphaned OST file without Exchange:

Download Univik OST Viewer (free) from this page
Install and launch the application
Click "Add OST File" and select your orphaned .ost file
The viewer opens it directly, no Exchange connection or Outlook profile needed

This works regardless of whether the original Exchange account still exists.

An OST file becomes "orphaned" when it loses connection to its original Exchange mailbox. This happens when:

You leave a job and your Exchange account is deactivated
Your Office 365/Microsoft 365 subscription expires
The Exchange server is decommissioned or migrated
Your Outlook profile is deleted or corrupted
You recover an OST file from an old computer/backup

Microsoft designed Outlook to require a valid Exchange connection to open OST files. Without that connection, Outlook blocks access, even though all your emails are still inside the file.

OST files are typically stored in these locations:

Windows 10/11: C:\Users\[Username]\AppData\Local\Microsoft\Outlook\
Office 365 accounts: Named as [email]@domain.com.ost
Exchange accounts: Named as [email]-[server].ost

Tip: Search your computer for *.ost to find all OST files. The AppData folder is hidden by default, enable "Show hidden files" in Windows Explorer.

Yes, if you have the OST file. When you leave a company, your Exchange account is typically deactivated. However, if you copied your OST file before leaving (or still have access to your old work computer's hard drive), OST Viewer can open it.

Important: Always check your company's IT policies and employment agreement. Some organizations consider work emails to be company property. OST Viewer is a tool, you're responsible for ensuring you have the legal right to access the data.

Yes. OST Viewer fully supports OST files created by:

Office 365 (all plans)
Microsoft 365 (Personal, Family, Business, Enterprise)
Exchange Online
Outlook for Microsoft 365

It works regardless of whether your Microsoft 365 subscription is currently active or has expired.

Yes, with proper credentials. If your OST file is encrypted, OST Viewer will prompt you to enter the appropriate credentials. Once authenticated, you can view all contents normally.

Note: OST Viewer does not bypass or crack encryption. You must have legitimate access credentials.

OST Viewer is specifically designed to handle the unique challenges of orphaned OST files, files that have lost their Exchange connection. It bypasses Outlook's Exchange verification.

PST Viewer opens PST files, which are already portable and don't have Exchange dependencies.

If you're unsure which viewer you need, check your file extension: .ost → OST Viewer, .pst → PST Viewer.

OST Viewer is designed for viewing OST files. You can save attachments and print emails, but it doesn't include conversion functionality.

If you need to convert OST to PST, MBOX, EML, or other formats, use our OST Converter tool which includes full export capabilities.

View All FAQs →

Download Free OST Viewer

Open orphaned OST files without Exchange Server. Access emails you thought were lost.

Download OST Viewer, Free

Version 5.8 | 22 MB | Windows 7/8/10/11 | No Exchange required

Opens Orphaned OST

No Exchange Needed

Read-Only Safe

Related Tools

Need more than just viewing? Check out these related products.

OST Converter

Convert orphaned OST to PST, MBOX, EML, PDF and 15+ formats.

Learn More →

PST Viewer

Open PST files without Outlook. Free PST file reader.

Learn More →

Universal File Viewer

View 50+ file formats including PST, OST, MBOX, EML.

Learn More →

Stuck with Orphaned OST Files?

Our support team specializes in OST file recovery. Get expert help with orphaned, encrypted, or problematic OST files.

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Univik OST File Viewer Access Emails after Exchange Disconnection

When OST files Become Inaccessible

Left Your Job

Office 365 Subscription Expired

Exchange Server Decommissioned

Outlook Profile Deleted or Corrupted

OST Recovered from Old Computer

Legal Discovery or Forensics

OST Viewer Facts

OST vs PST: What's the Difference?

Offline Storage Table

Personal Storage Table

How Exchange - OST Synchronization Works

What OST Viewer Can Do

Open Orphaned OST files

Encrypted OST Support

Complete Mailbox View

Attachment Recovery

Advanced Search

Full Email Rendering

Office 365 OST Support

Works 100% Offline

Read-Only Safety

Why Outlook Can't Open Your OST File

Microsoft's OST Design Philosophy

How to Open Orphaned OST files

Step 1: Locate Your OST File

Step 2: Download OST Viewer

Step 3: Install and Launch

Step 4: Add Your OST File

Step 5: Browse and Recover

How Users Recovered their Emails

System Requirements & OST Compatibility

System Requirements

Supported OST Versions

Additional OST Compatibility Notes

OST Viewer FAQs

How can I open an orphaned OST file without Exchange Server?

What makes an OST file "orphaned" and why can't Outlook open it?

Where are OST files stored on my computer?

Can I access my work emails after leaving a company?

Does OST Viewer work with Office 365 and Microsoft 365 OST files?

Can OST Viewer open encrypted OST files?

What's the difference between OST Viewer and PST Viewer?

Can I convert OST to PST using OST Viewer?

Download Free OST Viewer

Related Tools

OST Converter

PST Viewer

Universal File Viewer

Univik OST File Viewer
Access Emails after Exchange Disconnection