Clear Outlook Cache on a PC: Safe Steps for Windows

To clear Outlook cache on a Windows PC, first choose the cache that matches the problem: in classic Outlook, rebuild the account’s OST file for stale or damaged synced mail, or use File > Options > Mail > Empty Auto-Complete List to clear address suggestions. In new Outlook, try repairing or resetting the app in Windows Settings. These actions affect different data, so do not delete Outlook files indiscriminately.

What Outlook cache means

Outlook uses local data to make messages and other mailbox information available quickly, including when a connection is slow or temporarily unavailable. In classic Outlook, a Microsoft 365, Exchange, Outlook.com, or IMAP account commonly uses an OST file as an offline copy of synced mailbox data. Outlook updates that copy as it synchronizes with the mail server.

“Cache” can also mean saved address suggestions, temporary app data, or data held by a web browser. Clearing one type does not necessarily fix a problem with another. For example, deleting autocomplete suggestions will not repair a mailbox that is failing to synchronize. Likewise, clearing a browser’s cache is not the same as rebuilding a classic Outlook OST.

The key distinction is whether the information is safely stored somewhere else. A synced mailbox usually has a server copy, but local-only information may not. A PST file, often used by POP accounts or for archived mail, can contain the only copy of messages. Treat it as personal data, not disposable cache.

Check what is safe to remove first

Before changing files or resetting an app, confirm which Outlook version you use and whether your messages have finished syncing. Classic Outlook is the traditional Windows desktop program with a File tab. New Outlook is the newer Windows app and has a Settings gear rather than the same File-tab options. Outlook on the web runs in a browser.

Check Outlook’s connection status and allow pending mail to send and receive. Open important recent messages to confirm they are available.
If you have drafts, Outbox messages, or changes made while offline, connect to the internet and let Outlook synchronize before rebuilding its cache.
Back up important local data, especially PST files and any folders that are not part of a synced mailbox. Do not delete a PST to clear a cache.
Close Outlook before renaming or removing a data file. If it remains open in the background, the file may be locked or the change may not take effect.

If you are unsure whether a file is an OST or PST, do not guess based on its name. In classic Outlook, check File > Account Settings > Account Settings > Data Files to inspect the listed data files and their locations. The account type and file extension are useful clues, but important data should be backed up before you proceed.

Rebuild the cache in classic Outlook

Rebuilding an OST is a reasonable step when a synced account shows old information, search or folders behave inconsistently, or synchronization errors continue after Outlook has reconnected. The process removes the local offline copy so Outlook can create a fresh one from the server. It can take time, particularly for a large mailbox, and messages may not all appear immediately while synchronization is underway.

Make sure the account is online and give Outlook time to send pending messages and synchronize. Close Outlook.
Find the OST file. One common folder is %LOCALAPPDATA%\Microsoft\Outlook. To open it, press Windows key + R, enter that path, and press Enter. If the file is elsewhere, use the location shown under File > Account Settings > Account Settings > Data Files.
Identify the OST that belongs to the affected account. Rename that file—for example, add .old to its name—rather than deleting every file in the folder. If Windows says the file is in use, confirm Outlook is closed.
Open Outlook again and let it create and populate a new cache. Keep the PC connected while the mailbox downloads. Large mailboxes or limited internet connections can make this take a while.

Renaming is a cautious alternative to immediate deletion because it leaves the old file available temporarily. Once Outlook has synchronized and you have confirmed the expected information is present, you can remove the old copy if you no longer need it. If Outlook cannot recreate the file, or the account is not a normal server-synced mailbox, stop and investigate before removing anything else.

Clear saved address suggestions

If the issue is an incorrect name or email address appearing while you write a message, clear the Auto-Complete list instead of rebuilding the mailbox cache. In classic Outlook for Microsoft 365 on Windows, go to File > Options > Mail. Under Send messages, select Empty Auto-Complete List and confirm. Outlook will build suggestions again as you send messages.

To remove just one unwanted suggestion, start composing a message, type enough of the name for the suggestion to appear, and use the X beside that suggestion if it is shown. In versions where the suggestion is selected in the list, you can select it and press Delete. The exact suggestion controls can vary with the Outlook interface, so avoid clearing the entire list if only one entry is wrong.

Removing a suggestion does not delete the person from your contacts or address book. It clears a convenience list used during message addressing. The classic Outlook File > Options route does not apply to new Outlook, which has a different interface and account behavior.

Clear data in new Outlook or Outlook on the web

New Outlook does not use the same File > Options workflow for rebuilding a classic Outlook OST. If the Windows app is malfunctioning, first close and reopen it, check for updates, and try the Repair option if Windows offers it. On Windows 11, open Settings > Apps > Installed apps, find Outlook (new) or Microsoft Outlook, open its menu, and choose Advanced options if available. On Windows 10, the equivalent app controls are under Settings > Apps > Apps & features. The labels and availability can vary by Windows build.

In the app’s Advanced options, try Repair before Reset. Repair is intended to fix the app without the broader data-clearing effect of a reset. Reset can clear local app data and may require you to sign in and configure the app again. Mail stored in a synced online account remains on the mail server, but make sure any unsent or local-only information is safe before resetting. If Windows does not show these options, use the app’s available update or reinstall route rather than deleting unrelated Outlook files.

For Outlook on the web, browser cache and cookies are controlled by the browser, not by classic Outlook’s OST settings. Clearing them may sign you out of websites or remove other site data, depending on which options you select. Try a private browsing window or another browser first: if Outlook works there, the issue may involve browser data or an extension. Avoid clearing all browser data unless you understand what else will be removed.

Choose the fix that matches the symptom

A targeted fix is safer and faster than clearing everything. Use the symptom as a guide, while remembering that network, account, and service problems can resemble cache problems.

Wrong address appears while composing: remove the single Auto-Complete suggestion or empty the list in classic Outlook.
Classic Outlook shows stale synced mail or persistent folder-sync trouble: check the connection first, then consider rebuilding the affected account’s OST.
New Outlook crashes or will not load correctly: update or restart it, then try Windows Repair; use Reset only if needed.
Outlook on the web works in a private window but not the usual one: check extensions and browser site data before changing desktop Outlook files.
Mail is missing from every device: investigate the account, server, or deletion state rather than assuming a local cache is the cause.

For classic Outlook, Cached Exchange Mode is a separate setting that controls how much mail is kept offline; it is not a general-purpose “clear cache” button. Changing it can affect offline access and synchronization behavior. Do not switch it off and on as a first step unless you understand the effect and have a specific reason.

What clearing the cache changes—and what it does not

After an OST rebuild, Outlook may show fewer messages or incomplete search results until it has downloaded and indexed the mailbox again. That is usually a temporary consequence of rebuilding the local copy, not proof that the server mailbox was erased. Keep Outlook open and connected, and check the mailbox through Outlook on the web or another device if you need to verify that server-stored mail is still present.

Clearing autocomplete removes remembered address suggestions, not contacts. Resetting new Outlook affects the app’s local state, not the password or contents of a server mailbox, though it can mean signing in and setting preferences again. Clearing browser data can affect unrelated websites. None of these steps should be described as deleting all Outlook email, but local-only data and unsent work deserve special care.

Cache clearing also is not a substitute for account recovery, repairing a damaged PST, or fixing a full mailbox. If the same issue occurs after a fresh cache has synchronized, look for a server-side problem, an add-in or app fault, account settings, or a Windows/network issue. Repeating cache deletion without identifying the cause can waste time and create avoidable disruption.

Common problems and precautions

If Outlook says an OST is in use, check that the program is fully closed, including any Outlook process still running in Task Manager. Do not force-delete a locked file. If the OST returns but the same stale data remains, verify that you renamed the correct account’s file and that Outlook has completed synchronization. An OST may be recreated with a new filename or location, so judge success by the mailbox behavior, not by the old file’s return.

If messages are missing after a rebuild, check Outlook on the web or the provider’s mailbox before assuming they were deleted. Items that existed only offline may not have reached the server. If the account uses POP or the missing mail is in a PST, the OST rebuild instructions may not apply; preserve the PST and seek account-specific guidance.

For a work or school account managed by an organization, policies or custom profiles may affect Outlook storage and repair options. Contact the IT administrator before changing data files if the mailbox is business-critical or you cannot identify the correct account file. The same caution applies if Outlook repeatedly fails to synchronize after a rebuild.

Frequently Asked Questions

Will clearing Outlook cache delete my emails?
Rebuilding an OST for a fully synchronized server mailbox normally recreates the local copy from the server, rather than deleting the mailbox. However, unsent or local-only items may not be on the server. Back up or verify them first, and do not delete PST files as if they were disposable cache.

Where is the Outlook cache stored on a PC?
A common classic Outlook OST location is %LOCALAPPDATA%\Microsoft\Outlook, but the actual path can differ. Check File > Account Settings > Account Settings > Data Files in classic Outlook to see the listed file and location. New Outlook and browser Outlook manage local data differently.

How long does Outlook take to rebuild its cache?
There is no fixed time. It depends on mailbox size, connection speed, and how much information Outlook needs to download and index. Leave the PC online and allow synchronization to finish before deciding that the rebuild failed.

Should I delete an OST or a PST file?
Do not treat the two as interchangeable. An OST is commonly a rebuildable offline copy of a synced mailbox; a PST can hold mail or archives that exist only on that PC. If you cannot confidently identify the file and its contents, do not delete it.

Does clearing Outlook cache remove contacts?
Emptying classic Outlook’s Auto-Complete list removes suggested addresses, not contacts stored in an address book. Rebuilding a synced OST refreshes its local mailbox copy. Before resetting an app or working with local-only data, verify that important contacts and other information are synced or backed up.

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