Your Outlook OST file can fill up your primary drive, causing low storage warnings. This file is a local copy of your Microsoft 365 or Exchange mailbox data. This guide explains how to find your current OST file and move it to another drive.
You will learn the steps to safely relocate the file without losing any data. The process involves closing Outlook, moving the file, and updating your mail profile.
Key Takeaways: Locating and Moving Your OST File
- File > Account Settings > Account Settings > Data Files: Opens the dialog to see the exact file path of your current OST file.
- Control Panel Mail > Show Profiles > Data Files: An alternative path to find and manage your Outlook data files from Windows.
- Mail applet in Control Panel: The tool you must use to change the OST file location after moving the physical file.
Understanding the Outlook OST File
An OST file is an Offline Outlook Data File. It works with Microsoft 365 and Exchange Server accounts that use Cached Exchange Mode. This mode downloads a copy of your mailbox to your computer for faster access and offline use.
The file grows as your mailbox does, often reaching several gigabytes. By default, Windows places it in a hidden system folder on your C: drive. Moving it to a larger drive can free up critical system space.
Prerequisites Before Moving the File
You need administrator rights on your computer. Ensure you have enough free space on the target drive. You must also know your Outlook account password, as the profile may need to be reauthenticated. Close Outlook completely before starting.
Steps to Find and Move Your OST File
Follow these steps in order. Do not skip any step to avoid profile corruption.
- Find the current OST file location
Open Outlook. Go to File > Account Settings > Account Settings. Click the Data Files tab. Your account will be listed. Note the full path shown in the Location column for your OST file. - Close Outlook and open Windows File Explorer
Exit Outlook fully. Check the Task Manager to confirm Outlook.exe is not running. Open File Explorer and navigate to the folder path you noted. You may need to enable viewing of hidden items in the View tab. - Copy the OST file to the new location
In the folder, find the file named "outlook.ost" or similar. Select it. Copy the file and paste it into the desired folder on your new drive, for example, D:\OutlookData\. Do not move or delete the original file yet. - Open the Mail setup tool in Control Panel
Press Windows key + R, type "control" and press Enter. Search for "Mail" and open the Mail (Microsoft Outlook) applet. Click Show Profiles. Select your profile and click Properties. - Change the data file path in your profile
In the Properties window, click Data Files. Select your Exchange or Microsoft 365 account and click Settings. In the next window, click Browse. Navigate to and select the new OST file you copied to the other drive. Click OK. - Delete the old file and restart Outlook
After successfully changing the path and closing all setup windows, you can safely delete the original OST file from the old C: drive location. Open Outlook. It will now use the OST file from the new drive location.
Common Mistakes and Things to Avoid
Moving the File While Outlook is Running
If Outlook is open, the OST file is locked. Moving or renaming it will cause errors. Always verify Outlook is closed in Task Manager under the Processes tab before touching the file.
Editing the Registry Directly
Some guides suggest changing the OST file path via the Windows Registry. This is not recommended. The official Mail applet in Control Panel is the supported method and updates all necessary settings correctly.
Not Having a Backup Before Changing the Path
Always copy the file to the new location first. Only after you confirm Outlook works with the new path should you delete the original. This gives you a fallback if the profile update fails.
OST File vs PST File: Key Differences
| Item | OST File (Offline Outlook Data File) | PST File (Personal Folders File) |
|---|---|---|
| Primary Use | Local cache for Exchange or Microsoft 365 accounts | Local storage for POP3, IMAP accounts, or archive files |
| Sync Behavior | Continuously synchronizes with the mail server | No automatic sync; mail is downloaded or moved manually |
| File Location Change | Changed via Control Panel Mail applet | Changed within Outlook via Account Settings |
| Data Recovery | Server is primary source; OST can be recreated | PST file is the only copy; requires backup |
| Default Naming | Outlook.ost | Outlook.pst or Archive.pst |
You can now move your Outlook OST file to free up space on your main drive. Use the Mail setup in Control Panel to change the path safely. For related management, learn how to compact an OST file to reduce its size. A useful advanced tip is to create a new folder on your target drive named "OutlookData" before moving the file to keep your system organized.