How to Move or Restore an OST File on a New Drive

If you've just swapped in a new hard drive, upgraded to an SSD, or migrated to a new machine, there's a good chance Outlook is no longer pointing to your old mailbox data. Outlook doesn't simply "carry over" an OST file the way it might with a document you drag and drop - the OST is tied tightly to your Windows profile, your Exchange or Microsoft 365 account, and the exact folder structure Outlook expects to see. Move the drive without doing this correctly, and Outlook usually responds by starting a fresh local cache rather than reading the one you just copied over — that fresh cache begins empty and resynchronizes from the server, it doesn't mean your mailbox itself is empty.

That's the core problem this guide solves. We'll walk through how OST files actually work, the safe ways to relocate one to a new drive, what typically goes wrong, and how to recover your mailbox data when the file refuses to reconnect. If the old OST contains required data that the new profile cannot obtain from the server, preserve that file and evaluate it separately rather than repeatedly trying to attach it to the new profile.

What Actually Happens to an OST File When You Change Drives

An OST (Offline Storage Table) file is a local cache. When Outlook runs in Cached Exchange Mode, it keeps a synced copy of your Exchange or Microsoft 365 mailbox on your hard drive so you can read mail, check your calendar, and search contacts even when you're offline. Everything eventually reconciles with the server, which is why Microsoft has never treated the OST as a portable backup — unlike a PST, it's meant to stay put.

An OST is associated with one specific Outlook profile and mailbox — it isn't portable the way a PST file is. Copy the .ost file to a new drive, point a fresh Outlook profile at it, and Outlook will often reject it outright or start a new local cache at the destination instead - leaving your old data sitting there, technically intact but inaccessible to that profile. This is what's usually meant by an "orphaned" OST.

A few situations where this comes up constantly:

• You replaced a failing or full hard drive and want your mail history back.
• You're consolidating everything onto a new SSD for speed.
• IT is redistributing storage across departments, and mailbox data needs to move with it.
• A laptop was replaced, and the old drive was pulled out as a precaution before wiping it.

In every case, the goal is the same: get the mailbox data that's sitting on the old drive working again on the new one, without losing folders, attachments, or message history along the way.

Before You Start: Back Up First

This part gets skipped more often than it should. Before touching the registry or moving anything, copy the existing .ost file to a separate location - an external drive, a network share, wherever - and keep Outlook closed while you do it. If something goes sideways during the move, you want a fallback copy of the original file rather than a corrupted one. This step only takes a few minutes, but it gives you a safe copy to fall back on if the transfer runs into problems, instead of risking your only copy of the mailbox data.

Method 1: Create a New Profile and Point It at the Copied OST (Microsoft's Documented Method)

This is the procedure Microsoft actually documents for relocating an OST: copy the file, then set up a new profile that points at the copied file instead of trying to redirect the existing one.

1. Close Outlook completely.
2. Copy the existing .ost file to the new drive location you want to use. (If you'd rather let Outlook build a fresh cache instead of reusing this one, you can skip this step — see Method 3 below.)
3. Open Control Panel > Mail, then click 'Show Profiles' and 'Add' to create a new profile.
4. Configure your Exchange or Microsoft 365 account in the new profile. When you reach the data file step, select 'Browse' and choose the .ost file you copied in step 2 — or, if you're creating a new file instead, browse to the new location and enter a file name.
5. Select 'Finish' to complete account setup.
6. Back in Control Panel > Mail, select 'Always use this profile', choose the new profile, and click OK.

For the full Microsoft-documented steps and screenshots, see Cannot change the location of .ost file on Microsoft Learn.

Method 2: Relocate the OST Using the ForceOSTPath Registry Key

This is the method Microsoft documents for redirecting where Outlook creates the OST file for a new profile — it does not relocate the active OST of a profile that's already configured. See Microsoft's current documentation for the Outlook versions this applies to.

Editing the registry incorrectly can cause serious problems, up to requiring a system reinstall. Back up the registry before making changes, and follow these steps carefully:

1. Close Outlook fully - don't skip this, or the key won't take effect properly.
2. Press Windows + R, type regedit, and hit Enter.
3. Navigate to: HKEY_CURRENT_USERSoftwareMicrosoftOffice16.0Outlook (Swap 16.0 for 15.0 if you're on Outlook 2013; check Microsoft's documentation above if you're unsure which version key applies to your build.)
4. Right-click the ‘Outlook’ key, choose ‘New’ > ‘Expandable String Value’, and name it ForceOSTPath.
5. Double-click the new value and enter the full path to the folder on your new drive, e.g. E:OutlookData.
6. Close the Registry Editor and restart Outlook.

Because the value only applies to a new profile, you'll need to remove and re-add your account (or set up a new profile) for Outlook to actually build the OST at the new path. This will trigger a full re-download from the server - fine if your mailbox is fully synced.

Method 3: Let Outlook Rebuild the OST and Re-sync

Sometimes the simplest path is to not move the old file at all. If your mailbox is hosted on Exchange or Microsoft 365, Outlook can just build a fresh OST on the new drive and re-download everything from the server:

1. Set up your account in a new Outlook profile, pointing Cached Exchange Mode storage at the new drive.
2. Let Outlook fully synchronize - for large mailboxes, this can take a while, so plan around your connection speed and mailbox size. The new OST follows your current "Mail to keep offline" cache-range setting, so it may not download your entire historical mailbox even once syncing finishes.
3. Confirm folder counts and recent items match what you expect before decommissioning the old drive.

The catch: anything that hadn't synced to the server yet - drafts, certain categories, or items in a mailbox that's no longer connected to a live server - won't come back this way. That's exactly the scenario where you need to pull data directly from the old OST rather than relying on a fresh sync.

When the Old OST Won't Open on the New Drive

This is where most people actually land after trying the methods above. Common symptoms:

• Outlook says the data file "cannot be accessed" or can't be opened.
• The account shows as orphaned with no matching profile.
• Outlook builds a new, empty OST instead of reading the old one.
• The file is flagged as corrupted after being copied across drives.

None of this necessarily means your data is gone - it usually just means Outlook can't natively reconnect a relocated OST to its original mailbox.

This is where a dedicated recovery workflow becomes relevant. The EdbMails OST to PST Converter can scan a preserved OST independently of its original Outlook profile, preview readable mailbox data, and export the required content to PST when the old cache cannot be reused normally.

Recover the Old OST with EdbMails OST to PST Converter

If the mailbox/profile cannot be restored and required data exists only in the old OST, use the EdbMails OST to PST Converter to scan the preserved file and preview readable mailbox data.

Recover only the required folders or items, then export to PST or migrate directly to a supported mailbox destination.

 For the complete recovery and export procedure, see How to Convert OST to PST.

A Few Things Worth Checking After Moving an OST File

• Disk space - the new drive needs enough free space to hold both the OST and, if you're exporting, a PST copy as well. Running out of space mid-transfer can cause the copy or export to fail or leave an incomplete file — worth checking free space before you start.
• Keep the active OST local - a backup copy can live anywhere, but the working OST itself should stay on local or profile storage that Outlook supports. Network-hosted Outlook data files can introduce their own performance and reliability problems, so avoid making a network share the active location.
• Outlook version match - moving between very old and very new Outlook builds can introduce its own quirks with cached mode settings, separate from the drive move itself.
• Selective recovery - you don't always need everything back. If you only need certain folders or date ranges, exporting selectively saves time and disk space.

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Additional resources:

• EdbMails OST to PST Converter
• Recover and Export an Orphaned OST File
• Repair a Corrupt Outlook OST File
• Rebuild OST Files in Outlook
• How to Open an OST File inOutlook
• Import an OST File into Outlook
• Recover Outlook Mailbox After Windows Upgrade
• Fix Outlook OST Compatibility Issues