How to Change OST File Location In Microsoft Outlook (Without resync)

If you’re using Microsoft Outlook with an Exchange, Office 365, or Outlook.com account, chances are you’re dealing with an OST file. It’s a local cache of your mailbox — great for offline access, but not so great if you’re running low on disk space or switching to a faster drive.

The problem? Outlook doesn’t make it easy to move the OST file. And if you just delete it and let Outlook create a new one, you’re stuck resyncing everything — which can take hours.

Here’s how to change the OST file location without resyncing your entire mailbox.

Why You Might Want to Move Your OST File

• You’re migrating Outlook data to a new SSD
• The current drive is running out of space
• You want to keep all Outlook data on a separate partition
• You’re trying to streamline backups or file management

The Right Way to Move OST Without Resync

Outlook doesn’t give you a built-in option to change the OST file location directly. But there’s a workaround that actually works — and it skips the full resync.

⚠️ Before You Start:

• This method involves editing the Windows Registry. If you’re not comfortable with that, back it up first.
• These steps are for Outlook 2016, 2019, and Microsoft 365. Other versions might vary slightly.

Step-by-Step Instructions

1. Close Outlook Completely

Make sure it’s not running in the background (check Task Manager if needed).

2. Find Your Current OST File

• Press Windows + R, type control, hit Enter.
• Go to Mail > Email Accounts > Select your account > Data Files.
• Note the current path of the OST file. You’ll need it later.

3. Move the OST File

• Copy or move the OST file to your new desired location (e.g., D:\OutlookData\).
• Don’t delete the original yet — we’ll point Outlook to the new location first.

4. Edit the Registry

• Press Windows + R, type regedit, hit Enter.
• Navigate to: HKEY_CURRENT_USER\Software\Microsoft\Office\<xx.0>\Outlook Replace <xx.0> with your Outlook version:
  • Outlook 2016 = 16.0
  • Outlook 2013 = 15.0
  • Outlook 2010 = 14.0
• Right-click the Outlook key > New > Expandable String Value.
  Name it: ForceOSTPath
• Double-click it, and set the value to the folder path where you moved the OST file (e.g., D:\OutlookData\).

5. Start Outlook

• Outlook will now look for the OST file in the new location.
• If it finds the moved file, it will open it without resyncing the entire mailbox.

6. Delete the Old OST (Optional)

Once you’ve confirmed everything is working, you can safely delete the old OST file to free up space.

Wrap-Up

This method saves time and bandwidth — especially if your mailbox is huge. It’s not officially supported by Microsoft, but it’s solid if you follow the steps carefully. Just remember: always back up the registry and your data before making changes.

Need help automating this for multiple users or deploying it via GPO? Drop a comment or contact us — we can help.