How to Clear the Cache in Outlook on Windows and Mac

To clear Outlook’s local cache, use the option that matches what is causing trouble: in classic Outlook for Windows, empty the Auto-Complete list or rebuild the account’s OST file; in new Outlook, reset the app; and on Mac, reset the affected account if that option is available. Cache clearing can fix stale suggestions, display glitches, or sync problems, but it does not remove a server-stored mailbox. Before rebuilding a cache, make sure important messages and drafts have finished syncing.

What You’ll Need

Access to the Outlook account and, if prompted, its password or multifactor authentication method.
A working internet connection for Outlook to download cached mail and calendar data again.
For an OST rebuild on Windows, enough free disk space to download the account’s cached mailbox.
A few minutes to identify which Outlook app you use: classic Outlook, new Outlook, or Outlook for Mac. The menus and cache controls differ.

Step-by-Step

Identify the cache or symptom you need to address. Outlook keeps several kinds of local data. If old names appear when you address a message, clear the Auto-Complete list. If a Microsoft 365, Exchange, or IMAP mailbox is stuck, displays outdated folders, or fails to sync, rebuilding its offline cache may help. If the new Outlook app itself is misbehaving, use Windows’ app repair or reset controls. Clearing one kind of cache will not necessarily fix another.

First check which Windows app is open. Classic Outlook has the traditional ribbon and a File tab. New Outlook has a simplified interface and a Settings gear, and may be labelled “Outlook (new)” in Windows. On a Mac, use Outlook for Mac; its account controls are not the same as the Windows ribbon.
Check that recent work is saved and synced. In Outlook, open the Outbox and confirm there are no messages waiting to send. Check that recent messages, calendar changes, contacts, and drafts appear in the mailbox when you are online. If Outlook displays “Working Offline,” reconnect before rebuilding a cache. A cache is local working data, but changes that have not reached the mail server may exist only on that device.

This check is especially important for POP accounts and any folders or files stored only on the computer. Do not treat a local Outlook Data File with a .pst extension as a disposable cache. A PST can contain the only copy of older mail or other data.
Clear address suggestions in classic Outlook for Windows, if that is the problem. In classic Outlook, select File > Options > Mail. Under Send messages, select Empty Auto-Complete List, then confirm. Close the dialog and start a new message to check the result. Outlook will build the suggestions list again as you send messages.

This removes the saved suggestion list, not your contacts or messages. If you only want to remove one incorrect suggestion, start typing the name or address in the To field, use the arrow keys to highlight the suggestion, and press Delete. On Mac and in new Outlook, do not expect the classic Windows File > Options path; the available suggestion controls depend on the app version.
Rebuild a mailbox cache in classic Outlook for Windows when sync data appears stale. Quit Outlook completely. Open File Explorer and enter %LOCALAPPDATA%\Microsoft\Outlook in the address bar. Look for an .ost file associated with the affected account. If you are unsure which file belongs to the account, stop rather than renaming files at random; ask your administrator or use a separate Outlook profile to diagnose it.

Rename the relevant OST file, for example by adding .old to its name, rather than permanently deleting it. Start Outlook again. Outlook should create a fresh OST and download the account’s cached mailbox. Keep the computer online and allow the initial sync to finish; large mailboxes can take a while. If Outlook reports that it cannot open the account or does not create a new file, restore the original filename and investigate the profile before trying again.

Only use this procedure for a cache file, typically for a Microsoft 365, Exchange, or IMAP account. Do not rename or delete a PST. If the account uses POP, or you cannot confidently distinguish OST from PST, do not use this step without first confirming where the mail is stored.
Let Outlook finish syncing, then check the affected folders. After an OST rebuild, folders may appear empty or incomplete briefly while Outlook downloads their contents. Leave Outlook open and connected. Check the status bar for a syncing message, and test a few expected messages in the Inbox and other affected folders. Search can also take time to return complete results while the mailbox is being indexed or downloaded.

If you use Cached Exchange Mode, the amount of mail kept offline can affect how long the rebuild takes. You can still access older mail through the server when connected, even if it is not yet in the local cache. Avoid repeatedly closing Outlook or renaming the new OST during this first sync.
Repair or reset new Outlook for Windows if its app data is the issue. Close Outlook. In Windows 11, open Settings > Apps > Installed apps, find Outlook (new), select the three-dot menu, then choose Advanced options. Select Repair first; this attempts to fix the app without the more extensive reset. If the problem remains, return to the same page and select Reset. In Windows 10, the app controls are under Settings > Apps > Apps & features; select Outlook and open its advanced options if shown.

A reset can remove app-local settings or data and require you to sign in and let mail download again. Confirm your account is accessible and unsynced work is not being kept only in the app before resetting. These Windows controls apply to new Outlook, not the traditional desktop Outlook program.
Refresh an account’s cache in Outlook for Mac, if needed. In Outlook for Mac, open Tools > Accounts, select the affected account, and look for the account’s more-options menu (often shown as three dots) and Reset Account. Confirm only if you are ready for Outlook to rebuild its local copy and sync the account again. Depending on the Outlook version and account type, this control may not appear. Do not remove the account as a substitute unless you know how it is configured and have checked for local-only data.

Keep Outlook online after the reset and allow the mailbox to repopulate. If you cannot find the reset option, check Outlook’s version and account settings rather than deleting application files manually. Outlook for Mac menu labels and available controls can differ between builds.
Verify the fix and keep the cache intact afterward. Send a test message, check that new mail arrives, and confirm that the folders or suggestions that caused the problem now behave normally. If the issue returns, note whether it affects one account, one device, or Outlook across devices. That distinction helps identify whether the cause is local cache data, an account setting, or a mail-server problem.

Common Mistakes

Deleting a PST as if it were an OST. An OST is normally a rebuildable offline copy of a supported account. A PST may be the only home for locally stored mail, archives, or contacts. Check the extension before changing any file.
Resetting Outlook before checking unsynced work. A message in the Outbox, an offline draft, or a change made without a connection may not have reached the server. Connect and verify first.
Expecting one cache action to fix every symptom. Clearing autocomplete suggestions does not rebuild a mailbox, and rebuilding an OST does not necessarily remove a bad address suggestion.
Interrupting the first sync. A rebuilt cache can take time to repopulate. Repeatedly restarting Outlook or removing the new cache can prolong the problem.
Using Windows instructions on a Mac or in new Outlook. The classic Windows File > Options menus are not present in the same form in those apps.

Tips

Try the least disruptive fix first: restart Outlook, check connectivity, then clear a specific suggestion or repair the app before rebuilding a full mailbox cache.
Keep the device connected to a reliable network and power source during a large mailbox download. A slow initial sync does not automatically mean the rebuild failed.
If you manage several accounts, change only the cache for the account showing the symptom. This makes it easier to identify the cause and reduces unnecessary downloads.
For a work or school account, ask your Microsoft 365 administrator before changing files or resetting an app if your organization manages Outlook settings or retention.

Troubleshooting

Outlook does not recreate the OST: Confirm that Outlook is fully closed before renaming a file, then reopen it while connected to the internet. If no new OST appears, restore the original filename and check the account’s connection and Outlook profile. Do not remove other data files to force a rebuild.

The mailbox looks empty after the reset: Give it time to sync, check that the correct account is selected, and confirm Outlook is not working offline. Search the mailbox on the provider’s website, if available, to distinguish a download delay from missing server mail. Do not delete the renamed old file until you have verified the new cache and any needed local data.

Repair or Reset is missing: Make sure you selected Outlook (new) in Windows app settings. Classic Outlook is part of Microsoft Office and does not use the same app reset page. If a work device blocks these controls, contact your administrator.

The problem continues across devices: If the same message, folder, or sending problem appears in Outlook on the web or on another device, the cause may be account-side rather than a local cache. Check service status, account rules, storage limits, and any error messages, or contact your mail administrator or provider. Clearing the local cache again is unlikely to fix a server-side issue.

Frequently Asked Questions

Will clearing the Outlook cache delete my emails?
Usually, no: mail stored on a Microsoft 365, Exchange, or IMAP server can sync back after a cache rebuild. However, unsent or local-only items may not be on the server, and a PST can contain the only copy of data. Verify before resetting or changing files.

How long does Outlook take to rebuild its cache?
It depends on mailbox size, connection speed, and the offline mail range. Small accounts may repopulate quickly; a large mailbox can take hours. Keep Outlook online and avoid interrupting it while folders and search data return.

Can I clear Outlook’s cache without deleting my account?
Yes. The classic Windows autocomplete control clears suggestions without removing an account, and renaming an OST rebuilds a local mailbox cache while retaining the account setup. New Outlook’s app reset is more extensive, so try Repair first.

Should I clear the cache regularly?
No routine clearing is needed. Cache removal is a troubleshooting step for a specific issue, not regular maintenance. Clearing it unnecessarily can trigger a large re-download and temporarily make offline mail unavailable.

Does this clear the cache in Outlook on the web?
No. Outlook on the web runs in a browser, so its temporary files are managed by the browser rather than the desktop Outlook cache controls described here. Browser cache steps vary by browser and can sign you out of websites.

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