Clearing the Outlook cache is a fundamental maintenance task that resolves synchronization delays, interface glitches, and performance bottlenecks. When Microsoft Outlook stores temporary files to speed up access to frequently used data, these files can occasionally become corrupted or excessively large, leading to application freezes or outdated search results. This process is safe and does not delete emails, contacts, or calendar events, as these items remain synchronized with the mail server.

Why clearing the Outlook cache improves performance

The Outlook cache acts as a local storage bridge between the desktop application and the mail server. By keeping local copies of profile information, images, and attachment previews, the software reduces the number of requests sent to the server. However, over months of heavy usage, the cache can accumulate thousands of small files.

Common symptoms indicating a need for a cache reset include:

  • Search results failing to show the most recent emails.
  • Profile pictures or signatures appearing incorrectly or outdated.
  • Synchronization errors between the mobile app and the desktop client.
  • A noticeable delay when clicking between the "Inbox" and "Sent Items" folders.
  • The application consuming high CPU or memory resources even when idle.

From a technical standpoint, most Outlook data is stored in a file known as an Offline Storage Table (.ost). While the .ost file holds your actual mailbox content, the secondary cache folders (like RoamCache) hold metadata and temporary UI elements. Clearing these specific folders forces Outlook to fetch fresh data from the server, effectively "refreshing" the application's environment.

How to clear Outlook cache on Windows Classic version

The classic version of Outlook for Windows remains the most widely used enterprise email client. It stores its primary temporary data in a hidden system folder called "RoamCache." Manually purging this folder is often the most effective way to fix "sluggish" behavior.

Steps to purge the RoamCache folder

Before proceeding, ensure that Microsoft Outlook is completely closed. Check the system tray (near the clock) to confirm the icon is not present, as active processes can lock these files and prevent deletion.

  1. Press the Windows Key + R simultaneously to open the Run dialog box.
  2. In the text field, type or paste the following path: %localappdata%\Microsoft\Outlook and press Enter.
  3. Locate the folder named RoamCache and double-click to open it.
  4. Inside this folder, you will see numerous files starting with names like Stream_Autocomplete or Stream_Calendar. Press Ctrl + A to select every file in the folder.
  5. Right-click the selection and choose Delete. You can also use Shift + Delete to bypass the Recycle Bin and free up disk space immediately.
  6. Restart Outlook.

Upon restarting, the application may take slightly longer to load initially. This is normal behavior, as Outlook is rebuilding the local metadata and re-downloading essential synchronization files from the Exchange or IMAP server.

What if the RoamCache folder is missing?

In some enterprise environments or specific configurations, users might encounter an error stating that the path cannot be found. This usually happens if the "AppData" folder is set to "Hidden" by system administrators. To resolve this, go to File Explorer, click the "View" tab, and ensure the "Hidden items" checkbox is selected. If the path still does not exist, it may indicate that you are using the "New Outlook" version or a specialized web-wrapped version of the client.

How to clear cache in New Outlook for Windows

Microsoft's "New Outlook" is architecturally different from the classic desktop client. It is built on a web-based framework similar to Outlook.com. Because of this, the traditional file path methods do not work. Instead, you must access the developer tools or clear the application data via the Windows Settings menu.

Using the Developer Tools method

This method allows for a more surgical cleaning of the local storage that the web-wrapper uses.

  1. Press Windows Key + R to open the Run box.
  2. Type the command: olk.exe --devtools and press Enter.
  3. Outlook will open alongside a Developer Tools window (similar to what you see in Chrome or Edge).
  4. Within the DevTools pane, navigate to the Application tab.
  5. In the left-hand sidebar, look for the Storage section and expand Local Storage.
  6. Right-click on the entry for https://outlook.office.com and select Clear.
  7. Repeat this for Session Storage and IndexedDB to ensure a complete reset.
  8. Close the application and restart it normally.

Using Windows System Settings

For a simpler approach that handles the New Outlook app like any other Windows Store application:

  1. Open the Windows Settings app (Win + I).
  2. Navigate to Apps > Installed Apps.
  3. Search for Outlook (New).
  4. Click the three dots and select Advanced options.
  5. Scroll down to the Reset section and click the Reset button. This will wipe the app's cache and local settings, requiring a re-login.

How to clear Outlook cache on Mac

Outlook for Mac stores data in a SQL database rather than the .ost files found on Windows. Therefore, "clearing the cache" on macOS usually involves resetting the specific account or clearing the folder properties.

Clearing cache in New Outlook for Mac

The modern interface for macOS makes it very easy to reset a single account without affecting the entire application profile.

  1. Launch Outlook for Mac.
  2. Click on the Tools menu in the top bar and select Accounts.
  3. In the window that appears, select the email account that is experiencing issues.
  4. At the bottom of the left pane, click the three dots (...) or the gear icon.
  5. Select Reset Account.
  6. Outlook will prompt for confirmation. Once confirmed, the app will restart and re-sync all folders for that specific account.

Clearing cache in Legacy Outlook for Mac

If you are using the older "Legacy" version of Outlook for Mac, the process is localized to specific folders.

  1. Right-click (or Ctrl-click) the specific folder (e.g., Inbox) that is not syncing correctly.
  2. Select Properties from the context menu.
  3. On the General tab, click the Empty Cache button.
  4. Outlook will delete the local copy of that folder and download the data fresh from the server.

How to clear Outlook Web App (OWA) cache

When using Outlook via a browser (Chrome, Edge, Firefox, or Safari), "Outlook cache" is essentially your browser's temporary internet files. Issues with the web app—such as buttons not clicking or emails not loading—are almost always caused by browser-side data corruption.

Clearing browser cache for Outlook

To resolve web app issues, you should target the cached images and files:

  1. In your browser, press Ctrl + Shift + Delete (Windows) or Cmd + Shift + Delete (Mac).
  2. Set the time range to "All time" or "Last 7 days."
  3. Ensure "Cached images and files" and "Cookies and other site data" are checked.
  4. Click Clear data.
  5. Reload the Outlook website.

In our internal testing with Microsoft Edge, we have found that specifically clearing the "Hosted App Data" can fix persistent OWA login loops that a standard cache clearing might miss.

Targeting specific cache types in Outlook

Sometimes, you don't need to clear the entire cache. You might only have an issue with one specific feature.

How to clear Auto-Complete list cache

The Auto-Complete list is the list of suggestions that appear when you begin typing an email address in the "To" field. If an old or incorrect email address keeps appearing, you need to clear this specific cache.

  1. In Outlook, click on File > Options.
  2. Select the Mail tab on the left.
  3. Scroll down to the Send messages section.
  4. Click the Empty Auto-Complete List button.
  5. Confirm the action by clicking Yes.

Alternatively, you can delete individual entries by clicking the small "X" next to a suggestion when it appears while you are typing.

Cleaning the Forms cache

If you use custom forms or organizational templates and they are not loading correctly, clearing the forms cache is necessary.

  1. Go to File > Options > Advanced.
  2. Under the Developers section, click Custom Forms.
  3. Click Manage Forms and then select Clear Cache.

Clearing the Temporary Attachment cache

Every time you open an attachment, Outlook creates a temporary copy in a hidden folder. If this folder reaches its limit, you may find that you can no longer open any attachments.

  1. Open the Run dialog (Win + R).
  2. Type %temp% and press Enter.
  3. Look for folders starting with Olk and delete their contents. This safely removes temporary copies of documents you have already viewed.

The Nuclear Option: Deleting the OST file

If clearing the RoamCache and Auto-Complete lists does not solve the problem, the issue likely resides within the Offline Storage Table (.ost) file itself. This is the main database where your local mailbox data is kept.

Important Note: Do not delete your .ost file if you are using a POP3 account, as this may result in permanent data loss if the "Leave a copy on server" option is not enabled. For Exchange, Microsoft 365, and IMAP accounts, deleting the .ost is safe because the server holds the master copy.

Steps to rebuild the OST file

  1. Close Outlook.
  2. Open the Run dialog and type %localappdata%\Microsoft\Outlook.
  3. Locate the file ending in .ost (usually named after your email address).
  4. Right-click the file and select Delete. (If you are nervous, you can rename it to .ost.old instead).
  5. Restart Outlook.
  6. Outlook will display a message saying it is "Preparing a local copy" and will begin downloading all your emails from the server. Depending on your mailbox size and internet speed, this could take anywhere from a few minutes to several hours.

In our experience, recreating the OST file is the "gold standard" fix for persistent 0x8004010f errors or when the search index refuses to acknowledge new emails.

Troubleshooting common cache issues

Why can't I delete the files in RoamCache?

If Windows says the files are "in use," it means a background process is still accessing the Outlook data. This is often caused by:

  • Skype for Business or Microsoft Teams (which integrate with Outlook calendars).
  • Third-party add-ins (like Grammarly, Zoom, or CRM tools).
  • Search Indexer (Windows is currently indexing your mail). To fix this, open the Task Manager (Ctrl + Shift + Esc), find any "Outlook" or "Microsoft Office" processes, and click End Task.

How often should I clear the cache?

For a typical user, clearing the cache once every six months is sufficient to maintain peak performance. However, if you manage multiple shared mailboxes or high-volume public folders, you may need to do this more frequently, as these configurations tend to bloat the cache much faster.

Does clearing cache fix "Working Offline" issues?

Sometimes. If Outlook is stuck in "Working Offline" mode despite a stable internet connection, it might be due to a corrupted synchronization file in the cache. Clearing the cache and toggling the "Work Offline" button in the Send/Receive tab usually forces a reconnection.

Summary

Clearing the Outlook cache is a highly effective, low-risk troubleshooting step for resolving a wide array of performance and synchronization issues. Whether you are using the Classic Windows client, the New Outlook app, or macOS, the goal remains the same: removing outdated or corrupted temporary data to allow the software to sync cleanly with the mail server.

By targeting specific folders like RoamCache for UI issues or the .ost file for deeper database corruption, users can avoid the lengthy process of reinstalling the entire Office suite. Remember to always close the application fully before attempting to delete system files, and ensure you have a stable internet connection for the subsequent re-sync process.

FAQ

What happens after I clear my Outlook cache?

When you restart Outlook, the application will be empty for a few seconds as it connects to the server. It will then begin "Rebuilding the cache," which means it is downloading your email headers, calendar appointments, and contact list. Your computer might run a bit slower during this initial sync due to high network and disk activity.

Will I lose my signatures or rules?

No. Signatures and Rules are either stored on the mail server (for Exchange/O365) or in separate files within your Windows profile. Clearing the cache folders discussed in this guide does not impact these settings.

Does clearing cache speed up email delivery?

It does not change the speed at which the server receives mail, but it can speed up how quickly that mail appears in your interface by removing the "clutter" that causes the local client to lag.

Can I clear Outlook cache on my iPhone or Android?

On mobile devices, you cannot clear the "cache" in the same way you do on a PC. Instead, you must open the Outlook app, go to Settings, select the mail account, and tap Reset Account. If that fails, the standard procedure is to delete the app and reinstall it from the App Store or Google Play Store.

Is there a shortcut to open the Outlook folder?

Yes, using the %localappdata%\Microsoft\Outlook command in the Run dialog is the fastest shortcut to bypass navigating through hidden folders in your User directory.