According to Microsoft’s documentation, OST files are encrypted with your Windows credentials and tied to specific Outlook profiles, serving as synchronized caches rather than portable archives.
Can I import an OST file into Outlook?
OST files aren’t meant to be imported since they mirror your Exchange or Office 365 mailbox and automatically sync with the server; importing them would defeat their purpose.
Also, the Microsoft learn community says Outlook (classic and new) doesn’t have an OST import option, as they leverage cloud storage via Exchange Online for file management and utilization.
This encryption and profile binding protect your data if your PC or OST file is stolen, unlike exporting PST files, which are standalone and portable.
Understanding The Situation: Moving an OST File to a New Computer
| Scenario | Situation | Best Solution |
| 1 . You upgraded computers | You copied your old OST file, hoping to open Outlook OST file on another computer. | Recreate the OST file or convert to PST. |
| 2 . Exchange/IMAP account still active | You still have access to the same email account. | Recreate the OST file. |
| 3 . Lost access to email account | The account was deleted, or the server was offline. | Convert OST to PST . |
| 4. The old computer still works | You can still open Outlook on the old machine. | Export to PST. |
| 5 . Want to archive old data | You want to preserve messages permanently. | Convert OST to PST for archiving or use Outlook migration tools. |
How to Import OST File In Outlook? (Outlook 2021, 2019, 2016, and Office 365)
Method 1: Recreate OST File (When Your Account Still Works)
Instead of importing the old OST file, you let Outlook create a new one that syncs with your mailbox server, to import Outlook OST to Office 365.
How to create OST file in Outlook?
Step 1: Open Outlook
Step 2: Enter the same email address you used before and click Connect to add Your Email Account.
Outlook will detect and configure your Exchange or Office 365 account automatically.
Step 3: Outlook starts “Setting up your account…” and creates a new OST file in (C:\Users[YourName]\AppData\Local\Microsoft\Outlook).
Step 4: Outlook will download all your mailbox data. Wait for Sync to Finish
Step 5: Once sync is done, check your Inbox, Calendar, Sent Items, and custom folders. All your emails and items should reappear as before.
Note: Your old OST file isn’t needed anymore; it was just a cache. Since Outlook downloads everything from the server, you can safely delete the old OST to free up space.
Method 2: Export to PST from Original Computer (Then Import)
If you still have access to your old computer where the OST file works, this is your most reliable path to transferring Outlook to another computer.
Steps to Export OST Data to a PST File
Export the .ost file as .pst on your old computer:
Step 1: Open Outlook, ensure it’s fully synced (check the status bar).
Step 2: Go to File > Open & Export > Import/Export.
Step 3: Choose Export Settings, Select Export to a file > Next, and choose Outlook Data File (.pst) > Next.
Step 4: Pick What to Export. Select your main email account (top-level folder) and include subfolders, then click Next.
Step 5: Click Browse to choose where to save the PST File, click OK > Next, and click Finish.
Step 6: Transfer the PST File to a new computer using a USB drive, external hard drive, network, or cloud storage.
Import the .pst file on Your New Computer:
Step 1: Open Outlook > File > Open & Export > Import/Export.
Step 2: Select Import from another program or file > Next.
Step 3: Choose Outlook Data File (.pst) > Next.
Step 4: Browse to your transferred PST file.
Step 5: Select Replace duplicates with items imported > Next.
Step 6: Choose to import into your current mailbox and check Include subfolders
Step 7: Click Finish.
Method 3: Convert OST to PST Using Converter Tools
This is the method I turn to when you can’t access the original email account anymore, or when the old computer is inaccessible.
OST to PST converter tools can read your OST file and extract the data into an importable PST format.
Converter tools bypass Outlook entirely and read OST files directly.
These tools use specialized algorithms to decrypt and extract data from OST files without needing the original Outlook profile or server connection.
Remo OST to PST conversion tool converts OST to PST without Outlook and even if you cannot open the OST file.
Step 1. Download, install, and launch the Remo OST to PST Converter tool on your computer.
Step 2. Choose Open OST File (if you want to locate the OST file manually) or Find OST File (if you want the software to locate the OST file automatically) before clicking Next.
Step 3. Choose the Browse option to provide the destination path for the converted PST file and then click on Convert.
Step 4. The Remo OST converter tool now converts the OST file to a healthy PST file.
Method 4: Import OST File using Outlook Transfer Tool
Remo Outlook Backup and Migrate is an exclusive tool designed to back up Outlook data smartly and help you migrate Outlook across devices and versions.
Importing Outlook OST files is a no-brainer with this tool. Download the Remo Outlook Backup and Migrate tool for a swift OST importing process.
How to Create a Backup of your OST Files to Import into Outlook?
- Download and install the Remo Outlook Backup and Migrate tool on your system.
- Launch the software and click on the Backup Option.
- Depending upon your needs, you can choose between Smart Backup or Advanced Backup
- After you complete the backup process, click on the view report to verify the backup data.
- Save this backup file copy onto a USB or any other external drive to import the OST file onto another computer.
Now that you have successfully backed up your OST file, you can import the OST file onto another computer or on the same device after upgrading your Outlook version.
If you want to import OST files on the same computer, launch Remo Outlook Backup and Migrate, click on the Restore option, and select the Outlook backup file generated by the tool earlier.
Follow these suggestions to Smoothly Load OST file into Outlook.
- Update Outlook (File > Account > Update Options).
- Close all instances (Task Manager) before adding.
- Test with dummy data, import a folder first.
- Monitor space: OSTs balloon; defrag post-import.
- For multi-profiles: Export registry (regedit > Mail key)
Frequently Asked Questions
OST files are encrypted and tied to the Outlook profile and account that created them. If you move or copy the OST to another computer, Outlook won’t recognize it. To access its data, either reconnect the same account to recreate the OST or convert the file to PST format using a converter tool.
By default, OST files are stored in: C:\Users\AppData\Local\Microsoft\Outlook\
You can also find the location by opening Outlook > File > Account Settings > Account Settings > Data Files tab, then checking the path listed for your mailbox.
Outlook for Mac doesn’t support OST files. To use the data, convert the OST file into a PST file on a Windows system, then import that PST into Outlook for Mac via File > Import > Outlook for Windows archive (.pst).
Conclusion:
To conclude, I’ve learned that understanding why OST files can’t be imported directly is actually a better decision, avoiding cache issues and duplicates. Once you accept that OST files are synchronized caches rather than portable archives, the right solution becomes clear based on your situation.
