How to Delete OST File in Outlook on Windows 11: Step-by-Step Guide to Fix Errors

Outlook stores your emails and other data in OST files to allow offline access. Sometimes, these OST files can become corrupted or cause errors in Outlook. Deleting the OST file can help fix these issues by forcing Outlook to create a fresh copy.

This guide will walk you through the process of deleting an OST file on Windows 11 step-by-step. Even if you are not very technical, you will find the instructions easy to follow.

Before deleting the OST file, it’s important to understand what it does and why deleting it can solve problems. This article also covers some troubleshooting tips and frequently asked questions.

By the end, you should be able to fix common Outlook errors related to OST files and get your email working smoothly again.

Quick Note Before You Begin

Backup is not necessary: OST files are copies of your mailbox stored on the Exchange server, so deleting them does not delete your actual emails.
Close Outlook: Make sure Outlook is completely closed before deleting the OST file to avoid file access errors.
Know your Outlook version: These steps are for Windows 11, but the process is similar on other versions.
Check for synchronization: If your OST is linked to an Exchange or Microsoft 365 account, Outlook will recreate the file after deletion.

Step 1: Close Outlook

Before you delete the OST file, ensure Outlook is fully closed. This prevents any file corruption or access conflicts. To close Outlook:

Click the X on the Outlook window.
Check your taskbar to make sure no Outlook icon is visible.
If unsure, open Task Manager by pressing Ctrl + Shift + Esc, find Outlook.exe under the Processes tab, and click End Task.

Step 2: Locate the OST File on Windows 11

OST files are usually stored in a hidden AppData folder in your user profile. To find the OST file:

Press Windows + R to open the Run dialog box.
Type %localappdata%MicrosoftOutlook and press Enter.
A File Explorer window will open showing your Outlook data files.

Here, you should see one or more files with the .ost extension. These are your Outlook offline data files.

Step 3: Delete the OST File

Now that you have found the OST file, you can safely delete it. Deleting the OST forces Outlook to create a new file and resynchronize your mailbox.

Right-click the OST file you want to delete.
Select Delete from the context menu.
Confirm the deletion if prompted.

If you get a message saying the file is in use, double-check that Outlook is fully closed (refer back to Step 1).

Step 4: Restart Outlook

After deleting the OST file, open Outlook again. Outlook will detect the missing OST file and create a new one automatically. This process may take some time depending on your mailbox size.

Your emails and other mailbox data will be resynced from the server. This often resolves synchronization errors or corruption issues caused by the previous OST file.

Alternative Method: Using Outlook Account Settings

If you prefer not to manually locate the OST file, you can disable and re-enable the offline mode to reset the OST file:

Open Outlook.
Go to File > Account Settings > Account Settings.
Select your email account and click Change.
Uncheck the box that says Use Cached Exchange Mode.
Click Next and then Finish.
Close Outlook.
Reopen Outlook and repeat steps 1 to 4 to delete the OST file.
Then, re-enable Cached Exchange Mode by reversing the above steps.

Why Deleting OST Files Helps Fix Errors

OST files can become corrupted or out of sync due to many reasons, such as sudden shutdowns, large mailbox size, or connection issues. Deleting the OST file removes the corrupted copy and forces Outlook to download a fresh copy of your mailbox from the server.

This simple reset often fixes errors like sync problems, freezing, or missing emails.

Frequently Asked Questions (FAQs)

Will I lose my emails if I delete the OST file?

No. OST files are copies of your mailbox stored on the server. Deleting the OST file does not delete your emails. Outlook will recreate the OST file and resync all data.

Can I delete OST files for all email accounts?

Yes, but only for accounts configured with Microsoft Exchange, Microsoft 365, or Outlook.com. For POP or IMAP accounts, OST files are not used.

What if I can’t find the OST file?

Use the Run command %localappdata%MicrosoftOutlook to open the default folder. If you changed the file location, check your Outlook Account Settings or consult your system administrator.

Will Outlook work without the OST file?

Yes. Outlook will recreate the OST file automatically when it starts and connects to the server.

Is it safe to delete the OST file?

Yes, as long as your email account is connected to an Exchange or Microsoft 365 server, deleting the OST file is safe and often recommended for troubleshooting.

When Nothing Works

If deleting the OST file and restarting Outlook does not fix your problems, try these last options:

Repair Outlook: Use the built-in Office repair tool via Settings > Apps > Microsoft Office > Modify > Quick Repair.
Create a new Outlook profile: This can resolve profile corruption issues.
Contact support: Visit the official Microsoft Outlook support page for advanced help: Microsoft Outlook Support.

Conclusion

Deleting the OST file in Outlook on Windows 11 is a straightforward way to resolve many common errors related to synchronization and data corruption. By following the steps carefully—closing Outlook, locating and deleting the OST file, then reopening Outlook—you allow the program to create a fresh copy of your mailbox data.

Remember, OST files are just offline copies, so deleting them will not cause data loss. If problems persist, use advanced troubleshooting like repairing Office or creating a new profile. This guide provides an easy path to get Outlook back to smooth functioning.