How to Clear Cache in Outlook Email

To clear Outlook’s cache, use the method for the version you have: rebuild the Outlook data cache in classic Outlook for Windows, reset the app in new Outlook, reset the account cache on Mac, or clear site data for Outlook on the web. These steps remove local copies used to load or sync mail; they do not normally delete messages stored in your mailbox. Before starting, let Outlook finish syncing and check that anything important in Drafts or Outbox has been sent or saved.

What You’ll Need

A working internet connection and your Microsoft 365, work, or personal Outlook sign-in details. You may need to sign in again after a reset.
A few minutes for Outlook to download mail and folders again after its cache is rebuilt.
On Windows classic Outlook, permission to close Outlook and rename a local data file. Do not proceed if you have unsent or unsynced items you cannot risk losing.

Step-by-Step

Identify which Outlook you use. Classic Outlook for Windows has a traditional ribbon and a File tab. New Outlook for Windows has a simplified interface and usually a Settings gear. Outlook for Mac has Mac menus across the top of the screen. Outlook on the web runs in a browser at Outlook.com or Microsoft 365. Choose the matching section below; a cache-clearing method for one version may not exist in another.
Check sync and save anything local. In Outlook, check the Outbox and Drafts, and confirm that recent messages appear in the mailbox when you access it online or on another device. If Outlook says it is working offline, reconnect first. If a message is stuck in the Outbox, copy its text somewhere safe before resetting or rebuilding anything. A cache is a local working copy, but unsent changes may not yet exist on the mail server.
For classic Outlook on Windows, close Outlook completely. Exit the app, then wait several seconds. If it remains open in the background, press Ctrl+Shift+Esc to open Task Manager, select Microsoft Outlook if it is listed, and choose End task. Do not rename a data file while Outlook is using it.
Find the local Outlook data folder. Press Windows key+R, enter %LOCALAPPDATA%\Microsoft\Outlook, and press Enter. This opens Outlook’s local data folder in File Explorer. Look for an .ost file, which is typically a synchronized cache for a Microsoft 365, Exchange, or IMAP account. If you do not see an OST file, stop rather than guessing which file to remove.
Rename the OST file instead of deleting it. If you have confirmed that your mail and changes have synced, right-click the relevant .ost file, choose Rename, and add a suffix such as .old to its name. If Windows reports that the file is in use, Outlook has not fully closed. Do not rename or delete a .pst file: it can contain mail stored only on your computer, rather than a replaceable synchronized cache.
Open classic Outlook and let it rebuild. Start Outlook and sign in if prompted. Outlook should create a fresh OST and download the mailbox again. Depending on mailbox size and connection speed, folders and older messages may appear gradually. Keep Outlook open and online until syncing has had time to finish; avoid repeating the rebuild if it is simply still downloading.
For new Outlook on Windows, use the app reset. Close Outlook, open Windows Settings, and go to Apps > Installed apps. Find Outlook (new), select the three-dot menu, choose Advanced options, and select Reset. The wording or placement can differ slightly by Windows release. Start Outlook again and sign in. Reset clears local app data and settings, so expect to set up the app again; it does not serve as a way to erase mail from the mailbox.
For Outlook for Mac, reset the affected account. In Outlook, open Tools > Accounts, select the account that is having trouble, and choose the more-options button (or the account-management option) and Reset Account, if that option is shown. Confirm the reset, then allow Outlook to sync the account again. Menu names can vary with the Outlook for Mac version. If there is no reset option, check Outlook > Settings > Accounts for account-management choices or update Outlook before trying another method; do not remove an account unless you know its messages and drafts are safely on the server.
For Outlook on the web, clear only Outlook’s site data. In your browser’s privacy or site-data settings, search for the Outlook site you use—often outlook.office.com, outlook.live.com, or your organization’s Microsoft 365 address—and remove data for that site. In Chrome, site data is managed under Settings > Privacy and security; in Edge, use Settings > Cookies and site permissions. Close the Outlook tab, reopen the site, and sign in. Clearing site data can sign you out, so have your sign-in method available.
Clear the suggested-recipient list only if that is the problem. If Outlook is showing an incorrect address when you compose a message, that is usually the AutoComplete list, not the mail cache. In classic Outlook for Windows, start a new message, type a few letters in the To field, and use the X beside an unwanted suggestion to remove that entry. This removes a suggestion, not the contact or the mailbox message. Other Outlook versions may show suggestions differently.

After using the method for your version, send a test message to yourself and check that it arrives. Also open a few folders and verify that recent messages and attachments load. The first search or folder open may be slower while Outlook repopulates its cache.

Common Mistakes

Deleting the wrong data file. An OST can usually be rebuilt for a synced account; a PST may be the only copy of locally stored mail. Check the extension before changing anything, and make a backup if you are unsure.
Resetting before checking the Outbox. A message that has not reached the server may be lost when local app data is cleared. Copy its contents and attachments somewhere safe first.
Expecting a cache clear to fix every account problem. It will not correct an expired password, an account outage, a full mailbox, or a server-side delivery issue. Check your account online before rebuilding local data.
Clearing all browser data unnecessarily. Removing every cookie can sign you out of many sites. For Outlook on the web, target Outlook’s site data when the browser allows it.
Changing the Cached Exchange Mode slider and calling it a cache clear. That setting controls how much mail Outlook keeps available offline; changing it does not remove and rebuild the existing cache in the same way as renaming an OST.

Tips

Try the least disruptive fix first: restart Outlook, check your connection, and confirm the account works in a browser. Rebuild or reset local data only when a local sync or display problem remains.
Keep Outlook online after a reset. A large mailbox can take a while to download, and search results or older messages may be incomplete until synchronization finishes.
If you are unsure whether an item is stored on the server, verify it through Outlook on the web or ask your organization’s IT support before resetting the app or renaming a file.
Do not confuse clearing a cache with deleting mail. To remove a message from the mailbox, use Outlook’s normal delete controls; clearing local cache is intended to refresh the local copy.

Troubleshooting

Outlook will not reopen after renaming the OST. Check that the file was renamed rather than deleted and that you changed only an OST. Restart Windows, open Outlook, and give it time to create a new cache. If Outlook reports that the data file cannot be accessed, restore the original filename if possible and contact your administrator or Microsoft support before making further changes.

The OST is still reported as in use. Quit Outlook and look in Task Manager for any remaining Outlook process. End it only if you have saved your work and are sure Outlook is no longer syncing. A computer restart can also release a file handle; then try the rename again.

Mail is missing or the cache does not rebuild. Check the same mailbox in a browser. If the messages are missing there too, the issue is likely not just the local cache; check Deleted Items, filters, account settings, or ask your mail administrator. If the mailbox is online but Outlook remains empty, confirm that the correct account is selected and connected, then allow more time for synchronization.

New Outlook’s Reset option is unavailable or does not help. Confirm that you selected Outlook (new), not classic Outlook, in Windows Installed apps. Restart Windows and check for app updates. If the issue continues, use the organization’s support channel or Microsoft’s repair guidance rather than removing local files manually.

Outlook on the web still behaves strangely. Close all Outlook tabs, remove site data for the exact Outlook address, reopen the browser, and sign in again. If the problem continues, test Outlook in a private or InPrivate window. If it works there, a browser extension or broader browser setting may be interfering.

Frequently Asked Questions

Will clearing Outlook’s cache delete my emails?
Usually not, when you rebuild a synchronized OST, reset new Outlook, or clear Outlook website data. Those methods remove local copies or settings, while synced messages remain on the mail server. Unsent or unsynced changes are the exception, so check them first.

How often should I clear the Outlook cache?
There is no routine schedule. Clear or rebuild it when you have a specific local problem, such as stuck syncing, stale folder contents, or repeated loading errors. Doing it regularly adds download time without usually improving a healthy account.

Does clearing the cache free up mailbox space?
No. It may free space on your device, but it does not reduce the storage used by messages on the mail server. To free mailbox space, review and delete or archive mail using your organization’s retention rules.

How long will Outlook take to sync afterward?
It depends on the mailbox size, connection, and how much history Outlook is set to keep offline. Recent messages may appear before older mail or attachments. Leave Outlook online and check its sync status before deciding that the rebuild failed.

Is clearing the cache the same as clearing AutoComplete?
No. The cache supports local data and synchronization; AutoComplete stores suggested recipient addresses. Remove an incorrect suggestion from the recipient field rather than resetting the entire account cache.

Can I clear the cache without signing in again?
Not always. A Windows app reset or removal of Outlook website data can require you to authenticate again. Make sure you know the account password and can complete any multi-factor authentication before you begin.

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