How to Clear Cache Files in Outlook Safely

To clear Outlook’s local cache on Windows, close classic Outlook, rename the account’s .ost file, then reopen Outlook and let it rebuild and sync. An OST is an offline copy of mailbox data, not the mailbox itself. The right method depends on whether you use classic Outlook, new Outlook, Outlook for Mac, or Outlook on the web, so identify your version before removing anything. Never delete a .pst file as a cache-cleaning step.

What You’ll Need

A Windows or Mac computer with Outlook installed, plus permission to change files or reset the app.
Your work or personal account sign-in details and access to its internet connection. You may need to sign in again after resetting the app.
Time for Outlook to download mailbox data again. A large mailbox or a slow connection can make the first sync take a while.
If you use classic Outlook for Windows, a way to confirm the account is an Exchange, Microsoft 365, or IMAP account that syncs with a server. Do not rebuild its cache until you have checked that important messages and pending mail are synced.

Step-by-Step

Identify your Outlook version and what you want to clear. Classic Outlook for Windows has an offline data file, usually an .ost, that can be rebuilt. New Outlook for Windows has an app reset option. Outlook for Mac has a folder cache control in supported versions. Outlook on the web stores browser data rather than a local Outlook mailbox file. In classic Outlook, the File tab and ribbon are visible; new Outlook has a redesigned interface and a Settings button. If you are unsure, check the app name in the Start menu or the About section in its settings.
Check that your mailbox is synced before changing a cache. In Outlook, open important recent messages and check the Outbox for messages waiting to send. If you have been working offline, reconnect and use Send/Receive > Send/Receive All Folders in classic Outlook. Wait until syncing completes. Check important messages in Outlook on the web or your organization’s webmail too, if available. Items that exist only on this computer, unsent messages, or changes that have not reached the server may not be recoverable if you remove local data.
Close classic Outlook completely on Windows. Save your work, choose File > Exit, and wait a few seconds. If Outlook remains open, right-click the taskbar and open Task Manager to check whether Microsoft Outlook is still running. If it is, select the Outlook process and choose End task only after confirming the app has closed normally. Do not rename or remove a data file while Outlook is using it.
Find the correct offline data file. In classic Outlook, go to File > Account Settings > Account Settings, then open the Data Files tab. Look for the file associated with the account and note its full path and extension. An OST is typically a server-synced offline cache. A PST is a separate data file that may contain locally stored mail, archives, or POP account data; leave it alone. If the path is hard to locate, press Windows key + R, enter %LOCALAPPDATA%\Microsoft\Outlook, and press Enter. Match the filename and extension with the Data Files tab rather than choosing a file at random.
Rename the OST instead of permanently deleting it. In File Explorer, use the path you noted to find the OST. Right-click it, choose Rename, and add a temporary suffix such as .old to the filename. If Windows says the file is in use, recheck that Outlook has fully closed. Renaming gives you a chance to restore the file if you picked the wrong one; do not rename a PST. If you cannot confidently identify an OST, stop and ask your IT administrator or use Outlook’s built-in repair options instead.
Reopen Outlook and allow the cache to rebuild. Start classic Outlook and sign in if prompted. Outlook should create a new OST and download the server-synced mailbox. Keep the computer online, plugged in if practical, and Outlook open while the initial sync runs. Mail folders may fill gradually; a blank or incomplete folder immediately after launch does not necessarily mean messages have been deleted. Check that recent and older messages appear before removing the renamed file. Keep it temporarily until you have confirmed the mailbox is complete.
For new Outlook on Windows, use the app’s reset option instead. Close Outlook. In Windows 11, open Start > Settings > Apps > Installed apps, find Outlook (new), select the three-dot menu, then choose Advanced options > Reset. In Windows 10, go to Settings > Apps > Apps & features, select Outlook, choose Advanced options, then Reset if the option is available. Reset clears the app’s local data and may require you to set up or sign in to accounts again. It does not mean you should delete classic Outlook OST or PST files. Reopen the app and let connected accounts sync.
For Outlook for Mac, clear a folder’s cache where the control is available. In Outlook, Control-click or right-click the folder that is not updating, choose Properties, and select Empty Cache. The wording and availability can differ between legacy and newer Outlook for Mac versions. This clears the local copy for that folder so Outlook can download it again; it does not remove the folder from the mail server. If you do not see the control, update Outlook or consult your organization’s support rather than deleting profile folders by hand. Keep the Mac online and allow the folder to resync.
For Outlook on the web, clear only the browser’s site data if needed. There is no Outlook desktop OST to remove when you use Outlook in a browser. First refresh the page, sign out and back in, or try a private browser window to test whether the issue is browser-specific. If clearing browser data is necessary, remove cached data for the relevant Microsoft or Outlook site using that browser’s privacy settings. This may sign you out and clear site preferences, but it should not erase server-stored email. Avoid clearing all browser data unless you are comfortable losing other sites’ saved sessions.
Verify the result before cleaning up. Check that Outlook opens without an error, the affected folders show current messages, and you can send and receive a test message if appropriate. Confirm that important locally available items are present. Once the rebuilt cache is working and you are sure you do not need the renamed OST, you can delete that old file to reclaim disk space. If the problem returns, investigate synchronization, add-ins, account settings, or server status instead of repeatedly deleting the cache.

Common Mistakes

Deleting a PST because it looks like a cache. PST files can hold the only copy of archived, imported, or POP mail. Removing one can make that data disappear from Outlook. Check the extension and the Data Files tab first.
Clearing the cache before pending work has synced. Drafts, Outbox messages, and edits made offline may exist only on the computer. Reconnect and confirm synchronization, or save important content elsewhere, before rebuilding a cache.
Expecting the mailbox to appear instantly. A fresh OST begins largely empty and fills from the server. Closing Outlook repeatedly or interrupting the connection can prolong the sync and make folders look incomplete.
Using the classic Outlook file method on new Outlook or Mac. The apps store local data differently and have their own reset or folder-cache controls. Do not follow instructions to remove an OST if your version does not use that file.
Confusing cache with Auto-Complete suggestions. Suggested recipient names are not the mailbox cache. In classic Outlook for Windows, File > Options > Mail includes an Empty Auto-Complete List control. Using it removes suggestions, not messages, and is unnecessary for most sync problems.

Tips

Rename a cache file first and retain it until you have verified the rebuilt mailbox. This is safer than immediate permanent deletion and makes it easier to recover from choosing the wrong file.
For a work account, check with IT before resetting Outlook if the device is managed, the account uses special archiving, or you are uncertain whether data is stored on the server.
Make a note of the account name, file path, and any error message before you start. If you have multiple Outlook profiles or mail accounts, this helps prevent changing the wrong account’s data.
Use a stable internet connection during a rebuild. For a large mailbox, leave Outlook open and allow several hours if needed; download time depends on mailbox size, network speed, and organization settings.
Clear a cache to address a specific issue, such as stale folder contents or a damaged local copy. It is not routine maintenance, and deleting it will not necessarily improve Outlook’s speed if the cause is a full mailbox, an add-in, or a server problem.

Troubleshooting

Outlook says the file is in use: Exit Outlook and check Task Manager for any remaining Outlook process. If you cannot safely close it, restart Windows and rename the OST before opening Outlook again. Do not force-delete a file that Windows reports as locked.

The OST does not rebuild or Outlook shows a connection error: Confirm that the account can sign in through webmail and that the computer is online. Check for a service outage, VPN issue, or organization sign-in requirement. If the account is disconnected or the server cannot be reached, Outlook cannot download a fresh cache. Contact your administrator if you do not control the account settings.

Folders appear empty or old messages are missing: Give synchronization time, then use Send/Receive > Send/Receive All Folders in classic Outlook. Check the same folders in webmail to distinguish a local display problem from missing server data. If the missing items were stored only in a local PST, renaming an OST will not restore them; find the original PST or a backup and do not delete it.

The new Outlook reset option is missing: Confirm you selected the correct Outlook app in Windows Settings and that the app is up to date. Some work devices restrict reset controls. Ask your IT administrator for the approved repair process instead of manually removing app folders.

The Mac folder still will not update: Confirm Outlook is online, then try Empty Cache for the affected folder again and allow it to sync. If the control is unavailable or the issue affects many folders, update Outlook and check account status. Re-adding an account or rebuilding a profile can have wider effects, so get help before attempting either with unsynced data.

Frequently Asked Questions

Will clearing the Outlook cache delete my emails?
Rebuilding an OST for a connected Exchange, Microsoft 365, or IMAP mailbox normally makes Outlook download server-stored mail again. It is not a guarantee for items that were never synced or data stored only in a PST. Verify important items and pending messages first.

Is it safe to delete an OST file?
It is generally safe to rebuild a confirmed OST for a server-synced account after Outlook is closed and synchronization is complete. Renaming it first is more cautious. Do not apply this advice to a PST, and ask IT if you are unsure about the account or file.

How long does Outlook take to rebuild its cache?
It depends on mailbox size, connection speed, and settings. Recent messages may appear before older mail finishes downloading. Leave Outlook online and check progress over time rather than interrupting the initial sync.

Does clearing Outlook’s cache remove saved passwords?
It may prompt you to sign in again, particularly after resetting new Outlook or clearing browser site data. Have your credentials and any required multifactor authentication method available. Your organization may control sign-in behavior.

How do I clear Outlook cache on a Mac?
For a folder that is not syncing, Control-click or right-click it and choose Properties > Empty Cache when that option is present. The folder will need to download its contents again. Menu availability varies by Outlook for Mac version.

Can I clear the Outlook cache without deleting any files?
Yes. New Outlook for Windows offers an app Reset option, and supported Outlook for Mac versions offer Empty Cache for individual folders. For Outlook on the web, refresh or clear the browser’s site cache if necessary. Choose the method that matches the app you actually use.

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