Outlook OST File Rebuild Stuck at Updating Inbox: Fix

You started a mailbox repair or OST file rebuild in Outlook, but it freezes at the phrase “Updating Inbox” for hours. This leaves your email inaccessible and your calendar blank. The problem occurs when the local OST file is corrupted or when Windows Search tries to index a damaged item during the rebuild. This article explains why the rebuild stalls and provides four specific methods to force the process to complete.

Why the OST Rebuild Stalls at “Updating Inbox”

When Outlook rebuilds an OST file, it downloads a fresh copy of all mailbox data from the Exchange server or Microsoft 365. The process writes data to the local OST file in stages. The “Updating Inbox” phase is the longest because the Inbox typically holds the most items. The rebuild stalls when one of these conditions is true:

A single corrupt item in the Inbox causes the OST writer to hang. The item may be a message with a bad attachment, a malformed calendar invite, or a contact with invalid properties. Windows Search also indexes the OST while Outlook writes to it. If the search indexer tries to read a partially written item, the rebuild can freeze. The third cause is a damaged Outlook profile that cannot map the Inbox folder correctly during the sync.

Method 1: Rename the OST File and Let Outlook Recreate It

This is the fastest way to break the freeze. You rename the current OST file so Outlook creates a brand new file from the server data.

1. Close Outlook completely
   Press Ctrl+Alt+Delete and open Task Manager. End any Outlook.exe process that is still running. Wait 10 seconds.
2. Locate the OST file
   Open File Explorer and paste this path into the address bar: %localappdata%\Microsoft\Outlook. Press Enter.
3. Identify your OST file
   Look for a file with the .ost extension. The name usually matches your email address, for example user@domain.com.ost.
4. Rename the OST file
   Right-click the OST file and choose Rename. Add .old to the end of the filename, for example user@domain.com.ost.old. Press Enter.
5. Restart Outlook
   Open Outlook. It will display a message that it is creating a new OST file. This process can take 15 to 60 minutes depending on your mailbox size. Do not close Outlook during this time.

Method 2: Disable Windows Search Indexing for Outlook

If the rebuild still hangs after renaming the OST file, the search indexer may be the cause. Disable indexing for Outlook and then restart the rebuild.

1. Open Indexing Options
   Press the Windows key and type Indexing Options. Click the result.
2. Click Modify
   In the Indexing Options window, click the Modify button at the bottom.
3. Uncheck Microsoft Outlook
   In the list of indexed locations, find Microsoft Outlook. Uncheck the box next to it. Click OK.
4. Rebuild the OST file again
   Close Outlook, rename the OST file as described in Method 1, and restart Outlook. With indexing disabled, the rebuild should complete without freezing.
5. Re-enable indexing after the rebuild
   After the OST file finishes rebuilding, go back to Indexing Options, click Modify, and check Microsoft Outlook again. Click OK.

Method 3: Repair the OST File with Scanpst.exe

The Inbox Repair Tool can fix corruption inside the OST file without deleting it. Run this tool before attempting another rebuild.

1. Close Outlook
   Make sure Outlook is not running. Check Task Manager for any Outlook.exe processes.
2. Find Scanpst.exe
   Go to C:\Program Files (x86)\Microsoft Office\root\Office16 for Microsoft 365 or Office 2019. For Office 2016, use C:\Program Files (x86)\Microsoft Office\Office16. Double-click Scanpst.exe.
3. Browse to your OST file
   Click the Browse button. Navigate to %localappdata%\Microsoft\Outlook and select your OST file. Click Open.
4. Start the scan
   Click Start. The tool scans the file and reports any errors. If errors are found, click Repair. A backup file with a .bak extension is created automatically.
5. Restart Outlook
   Open Outlook. If the rebuild resumes, let it complete. If it freezes again, rename the OST file and let Outlook create a new one.

Method 4: Create a New Outlook Profile

A damaged profile can cause the rebuild to hang even after the OST file is replaced. A new profile forces Outlook to rebuild the entire mail configuration.

1. Open Mail in Control Panel
   Press Windows+R, type control, and press Enter. Change View by to Large icons. Click Mail (Microsoft Outlook).
2. Click Show Profiles
   In the Mail Setup window, click Show Profiles.
3. Add a new profile
   Click Add. Type a name for the new profile, for example Work2. Click OK. Enter your email address and password. Wait for the initial sync to finish.
4. Set the new profile as default
   In the Mail dialog, under When starting Microsoft Outlook, select Always use this profile. Choose the new profile from the dropdown list. Click OK.
5. Restart Outlook
   Open Outlook. It uses the new profile and creates a fresh OST file. The rebuild should complete without freezing.

If Outlook Still Has Issues After the Main Fix

Outlook freezes again after a few days

A recurring freeze indicates that a specific item on the server is causing the problem. Move all items from the Inbox to a subfolder or archive folder using Outlook Web App. Then delete the OST file and let Outlook rebuild it. If the rebuild completes, move items back in batches of 50 to identify the corrupt item.

OST file grows too large and rebuild fails

Outlook has a 50 GB OST file size limit. If your mailbox exceeds this, the rebuild may fail. Use the Mailbox Cleanup tool in Outlook to delete old items or move them to a PST file. After cleaning, rename the OST file and restart Outlook.

Error message “Cannot open your default email folders” after rebuild

This error means the new OST file was created but the profile cannot load it. Delete the new OST file, then run Scanpst.exe on the backup .bak file created earlier. After repair, restart Outlook. If the error persists, create a new profile as described in Method 4.

Item	Rename OST File	Create New Profile
Description	Deletes the local cache and forces a fresh download from the server	Creates a new mail configuration with a clean OST file
Time required	5 minutes setup + download time	10 minutes setup + download time
Preserves local rules	Yes, rules are stored on the server	Yes, rules sync from the server
Preserves local signatures	No, signatures must be recreated	No, signatures must be recreated
Fixes corrupted profile	No	Yes
Fixes corrupted OST item	Yes, by replacing the entire file	Yes, by replacing the entire file

You can now force an OST rebuild that was stuck at Updating Inbox to complete. Start with renaming the OST file, then disable Windows Search if the freeze returns. Run Scanpst.exe before creating a new profile to avoid losing any recoverable data. Use the Mailbox Cleanup tool regularly to keep your OST file under 50 GB and prevent future rebuild failures.