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How to Add an OST File to Outlook: A Comprehensive Guide

Adding an OST (Offline Outlook Data File) to Outlook isn’t as straightforward as dragging and dropping. It’s more like a surgical procedure for your email data. You don’t directly add an OST file in the same way you’d add a PST file (Personal Storage Table). The relationship is inherent: the OST file is linked to your Exchange, IMAP, or Outlook.com account and essentially acts as a cached copy of your mailbox on the server. However, scenarios arise where accessing or “adding” the data within an OST becomes crucial. This guide will walk you through the process and address common issues.

Understanding OST Files and Their Role

Before diving into the “how-to,” let’s clarify what an OST file actually is. Think of it as your Outlook mailbox’s trusty sidekick, holding all your emails, calendar events, contacts, and tasks for offline access. This allows you to work on your emails even without an active internet connection. Changes you make are synchronized with the mail server the next time you connect. The beauty of the OST file is its automatic creation and management by Outlook when you configure an Exchange, IMAP, or Outlook.com account. This means you don’t manually create one unless something has gone sideways and you need to troubleshoot.

The “Adding” Dilemma: Accessing Data Within an OST File

Since you can’t “add” an OST like a PST, the process revolves around re-establishing the connection between Outlook and the account associated with that OST. The key is understanding that you’re not adding the file itself; you’re re-linking to the data it contains.

Scenario 1: Reconnecting to the Original Account

This is the ideal and most common scenario. If you have access to the original Exchange, IMAP, or Outlook.com account, follow these steps:

Ensure Outlook is Closed: This is crucial to avoid conflicts.
Control Panel Navigation: Open the Control Panel. (Search for it in the Windows search bar).
Mail Setup: Select Mail (Microsoft Outlook 2016) (32-bit) or a similarly named option depending on your Outlook version. If you can’t find it, switch the Control Panel view to Large icons or Small icons.
Show Profiles: Click Show Profiles…
Add a Profile: Click Add… and name the new profile (e.g., “My Exchange Profile”).
Account Setup: Enter your name, email address, and password for the original account. Outlook will attempt to automatically configure the account.
Complete Setup: Follow the on-screen prompts. Outlook should now rediscover and connect to your account, rebuilding a new OST file. Note: You may need to manually configure server settings if auto-discovery fails. Obtain these settings from your email provider or IT administrator.
Set as Default (Optional): In the Mail Setup window, you can choose to always use this profile or be prompted to select a profile each time you open Outlook.

Why this works: This process forces Outlook to recreate the connection to the mail server, creating a new OST file. The mail server then synchronizes all your emails, contacts, and calendar items to this new OST.

Scenario 2: Orphaned OST Files – Conversion Required

An “orphaned” OST file is one that’s no longer associated with an active account. This often happens when an employee leaves a company, or an account is deleted. Directly accessing the data within an orphaned OST is impossible through Outlook itself. You need to convert the OST file to a PST file first.

Understand the Limitations: Microsoft does not provide a built-in tool for OST to PST conversion.
Third-Party Conversion Tools: You will need a reliable third-party OST to PST converter tool. Several options are available, ranging from free (often limited in functionality) to paid. Research carefully and choose a reputable tool.
Conversion Process: Follow the instructions provided by the chosen conversion tool. These tools typically allow you to select the OST file and specify a location to save the converted PST file.
Import the PST: Once the OST is converted to a PST, you can easily import it into Outlook:
- Open Outlook.
- Go to File > Open & Export > Import/Export.
- Select Import from another program or file and click Next.
- Choose Outlook Data File (.pst) and click Next.
- Browse to the location of the PST file you created and click Next.
- Choose how to handle duplicates (e.g., replace duplicates with items being imported, allow duplicates to be created).
- Click Finish.

Important Note: Converting OST files, especially large ones, can be time-consuming. Ensure your computer has sufficient resources and do not interrupt the process.

Scenario 3: Using an OST File on a Different Computer

You cannot simply copy an OST file to a different computer and expect it to work. OST files are tied to the user profile and machine on which they were created. Trying to directly open it on another computer will likely result in errors. The solutions are the same as above: either reconnect the original account (Scenario 1) or convert the OST to a PST (Scenario 2). Reconnecting the account is almost always preferable if possible.

Troubleshooting Common OST Issues

Outlook Won’t Open/Crashes: A corrupted OST file can prevent Outlook from opening. Try the ScanPST.exe tool (Inbox Repair Tool) located in the Office installation directory (usually C:Program FilesMicrosoft OfficerootOffice16 or similar, depending on your Office version). Run ScanPST.exe on the OST file. This tool is designed to repair minor corruption issues.
“Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. Errors have been detected in the file…”: This is a classic sign of OST file corruption. Run ScanPST.exe. If that doesn’t work, recreate the OST file by reconfiguring the account (Scenario 1).
Synchronization Problems: If your emails aren’t syncing correctly, check your internet connection. Also, try restarting Outlook. In more severe cases, consider recreating the OST file.
Large OST File Size: Archive older emails to reduce the OST file size. Consider using online archive solutions offered by Microsoft or your email provider.
OST File Location: The default location is typically in the C:Users%username%AppDataLocalMicrosoftOutlook folder.
Permissions Issues: Ensure you have full read/write permissions to the OST file and the folder it resides in.

FAQs: Adding OST Files to Outlook

1. Can I open an OST file without Outlook?

No, you can’t directly open an OST file without Outlook or a specialized OST viewer or converter tool. The data is stored in a proprietary format.

2. Is it safe to use free OST to PST converters?

Use caution. Some free tools may contain malware or may not accurately convert the data. Research thoroughly and read reviews before using any free converter. Paid tools often offer better support and are generally more reliable.

3. Will converting an OST to PST lose any data?

A reliable converter tool shouldn’t lose data. However, corruption within the OST file before conversion can lead to data loss. It’s always wise to back up the OST file before attempting conversion.

4. How long does it take to rebuild an OST file?

The time depends on the size of your mailbox and your internet connection speed. A small mailbox may take minutes, while a large one could take hours or even days.

5. What’s the difference between OST and PST files?

OST files are linked to Exchange, IMAP, or Outlook.com accounts and are synchronized with the server. PST files are local storage files and are not automatically synchronized. PST files are typically used for archiving or importing/exporting data.

6. Can I have multiple OST files in Outlook?

Yes, you can have multiple OST files if you have multiple Exchange, IMAP, or Outlook.com accounts configured in Outlook. Each account will have its own OST file.

7. What happens if I delete an OST file?

Outlook will recreate a new OST file when you restart it, provided the associated account is still configured. If the account is removed, the OST file becomes orphaned.

8. How do I find the location of my OST file?

In Outlook, go to File > Account Settings > Account Settings. Select your Exchange/IMAP/Outlook.com account, then click Change. In the Change Account window, click More Settings. In the Microsoft Exchange/Internet Email window, click the Advanced tab. The OST file location is displayed under Cached Exchange Mode Settings or similar.

9. Can I move an OST file to a different location?

Moving an OST file manually is not recommended. It can lead to corruption and synchronization issues. Let Outlook manage the location. If you must change it, do it through the registry with extreme caution and only if you are technically proficient. There are many guides online detailing how to do this, but again, it’s risky.

10. What is ScanPST.exe and how do I use it?

ScanPST.exe (also known as the Inbox Repair Tool) is a utility provided by Microsoft to repair minor corruption issues in OST and PST files. You can find it in the Office installation directory. Run the tool, select the OST file, and click Start. The tool will scan the file for errors and attempt to repair them.

11. My OST file is constantly growing. How can I manage it?

Archive older emails to a PST file, use online archiving solutions, or reduce the amount of data cached locally by adjusting the “Mail to keep offline” setting in Outlook.

12. What are the best practices for managing OST files?

Regularly archive older emails, ensure you have a stable internet connection, and avoid abrupt shutdowns of Outlook while it’s synchronizing. If you suspect corruption, run ScanPST.exe proactively.