Clear Outlook Desktop Cache: Safe Steps for Windows & Mac

To clear the cache in classic Outlook for Windows, first identify what is causing the problem: use File > Options > Mail > Empty Auto-Complete List to clear suggested email addresses, or close Outlook and rename its offline Outlook data file (.ost) to make Outlook rebuild the synced mailbox cache. In new Outlook for Windows, use Windows app settings to repair or reset the app instead; these methods affect different data, so choose the one that matches the problem.

What Outlook desktop cache means

Outlook uses the word cache for several kinds of stored information. In classic Outlook, the most important is the Offline Outlook Data File, or OST. With a Microsoft 365, Exchange, or other supported account, Outlook can keep a local copy of mailbox content so you can work while offline and see messages quickly. When connected, Outlook synchronizes changes between that local copy and the mail server.

Other stored data has a different purpose. Auto-Complete suggestions are addresses Outlook offers as you type in the To, Cc, or Bcc field. They are not the same as contacts in the People or Contacts folder. Outlook for Mac can also maintain a local folder cache, while new Outlook for Windows stores app data differently from classic Outlook.

Clearing a cache is therefore not one universal operation. Removing address suggestions will not repair a damaged mailbox cache, and rebuilding an OST will not necessarily remove an unwanted suggested address. Select the smallest action that addresses the symptom.

Before clearing anything

Check which Outlook you have. Classic Outlook for Windows has a File tab in its ribbon. New Outlook for Windows has a simplified interface and a Settings gear, and may be labeled Outlook (new) in Windows. The steps for an OST file apply to classic Outlook, not new Outlook.

Before resetting or rebuilding data, make sure the mailbox is connected and has finished synchronizing. Check the Outbox for messages that have not sent, and confirm that important messages, calendar items, and contacts appear in Outlook on the web or another device. This matters because a local-only item or an unsent message might not yet exist on the server.

Close Outlook before renaming or moving an OST file.
Do not delete a PST file as if it were a disposable cache. PST files can hold the only copy of archived or locally stored mail.
Expect the first synchronization after a rebuild to take time, especially for a large mailbox or a slow connection.
If your device is managed by an employer or school, follow its IT guidance before resetting an account or app.

Clear Auto-Complete suggestions in classic Outlook

If Outlook suggests an outdated or incorrect email address, clear the Auto-Complete list rather than rebuilding the mailbox. In classic Outlook for Microsoft 365 on Windows, open File > Options > Mail. Under Send messages, select Empty Auto-Complete List, then confirm. The list will start to populate again as you address future messages.

To remove just one suggestion, start a new message and type enough of the name or address for the unwanted suggestion to appear. Select the suggestion, then choose the X beside it if shown, or use the Delete key while the suggestion is selected. The exact interaction can vary slightly with Outlook updates and input devices.

Clearing Auto-Complete does not delete a person from your Contacts folder, remove messages, or change the address book on your organization’s server. If an address keeps appearing after you clear the list, check whether it is being supplied by a saved contact or your organization’s directory instead.

Rebuild the offline cache in classic Outlook for Windows

Consider rebuilding the OST when classic Outlook repeatedly reports synchronization errors, shows stale mailbox contents despite a working connection, or behaves as if its local mailbox copy is damaged. A rebuild makes Outlook download a fresh local copy. It is more disruptive than clearing suggestions, and it does not itself repair a server outage, account permission problem, or network issue.

Make sure Outlook is online and allow it to finish sending and receiving. Check the Outbox and verify that important recent items are visible in the web mailbox.
Exit Outlook. If it remains open in the background, use Task Manager to check that Outlook has closed before proceeding.
Press Windows key + R, enter %LOCALAPPDATA%\Microsoft\Outlook, and press Enter. This opens the usual folder for Outlook data files.
Find the OST associated with the account. If there are several files and you are unsure which is which, do not guess: record the file names and ask your administrator or Microsoft support for help.
Rename the relevant OST, for example by adding .old to its name. Renaming is a cautious alternative to immediately deleting it; do not rename or remove a PST file.
Open Outlook and let it create a new OST and synchronize. Keep the computer connected to the internet; a large mailbox may take a while to download.

The OST is normally a synchronized working copy for supported Exchange-based accounts, but that is not a reason to assume every unsynchronized change is safe. A message in the Outbox, an item created offline, or a local-only folder deserves particular care. If Outlook cannot reconnect after the rebuild, restore the renamed file only after closing Outlook and seek help rather than repeatedly deleting files.

Clear or repair cache in new Outlook for Windows

New Outlook does not use the same user-managed OST workflow as classic Outlook. If it is slow, fails to display current mail, or repeatedly glitches, first try closing and reopening it and checking that the account is online. You can also use the app’s repair option before resetting it.

In Windows 11, open Settings > Apps > Installed apps, find Outlook (new), select the three-dot menu, then choose Advanced options. If available, select Repair first. Repair is intended to fix the app without the broader data reset. If that does not help, return to the same page and select Reset. In Windows 10, the corresponding route is generally Settings > Apps > Apps & features, then Outlook’s advanced options.

A reset can remove local app data and require you to sign in or set up the account again. Mail and other server-synced information should become available after the account reconnects, but do not rely on that for unsent or otherwise unsynchronized content. If you do not see Advanced options, your Outlook installation or Windows configuration may differ; use the available Microsoft Store or Windows app repair controls, or ask your administrator.

Outlook for Mac: empty a folder cache

On Outlook for Mac, a common targeted action is emptying the local cache for a particular mail folder, where the option is available. In Outlook, Control-click or right-click the folder in the folder list and open Folder Properties. If the dialog includes Empty Cache, use it for that folder, then allow Outlook to synchronize its contents again. This is useful when one folder appears out of date, but it is not the same as deleting the account or its server-side mail.

Outlook for Mac’s menus and available cache controls differ between legacy Outlook and newer builds. If you cannot find Folder Properties or Empty Cache, do not substitute a random Library-folder deletion: first install available Office updates, check whether Outlook is in legacy or new mode, and consult the current Microsoft support instructions for that version. Removing and adding an account or profile is a broader reset and should be a later troubleshooting step, after checking that all needed data is synchronized.

Choose the fix that matches the symptom

Clearing cache can be unnecessary when the cause is elsewhere. A server outage, a full mailbox, a disconnected account, a filtering rule, or a slow network can all make mail appear missing or late. Compare Outlook with Outlook on the web: if the same message is missing in both, rebuilding a local cache is unlikely to solve the underlying issue.

Wrong address appears while composing: remove the Auto-Complete suggestion or check the saved contact.
Classic Outlook shows stale folders or synchronization errors: check connectivity and sync status, then consider rebuilding the OST if the server copy is intact.
New Outlook crashes or behaves inconsistently: try Repair, then Reset only if needed.
One Mac folder is stale: use Empty Cache for that folder if the option exists, then allow it to sync.
Mail is missing both online and in Outlook: investigate account, server, retention, or mailbox issues rather than deleting local files.

Also distinguish an Outlook cache from Windows credential storage, browser cache, and Office document cache. Removing saved sign-in credentials may trigger authentication prompts or disrupt other Office apps, while clearing a browser cache affects browser data; neither is a general Outlook mailbox-cache fix. Avoid broad cleanup utilities that claim to remove every Office cache unless you know exactly what they will delete.

What to expect after a cache reset

After an OST rebuild or folder-cache refresh, Outlook may show fewer messages at first and then fill in as synchronization proceeds. Search results, shared folders, attachments, or older mail can take longer to become available depending on account settings and the amount of data. Leave Outlook open and connected long enough for synchronization to complete before deciding that the reset failed.

If the same error returns, note its wording and when it occurs. Check Outlook’s connection status and whether Outlook on the web works, then contact your organization’s support team if it is a managed account. Repeating resets without diagnosing the cause can waste time and may increase the risk of losing a change that had not synchronized.

Frequently Asked Questions

Does clearing Outlook cache delete my emails?
Clearing Auto-Complete removes address suggestions, not email. Rebuilding a classic Outlook OST removes the local cached copy and downloads mailbox data again, but unsynchronized changes need special care. Confirm important items are present online before resetting.

How often should I clear the Outlook cache?
There is no routine schedule for clearing it. Outlook’s cache supports offline access and synchronization, so leave it alone unless you have a specific symptom such as stale content, a synchronization problem, or an incorrect address suggestion.

Will rebuilding the OST delete my contacts?
Contacts synchronized with the account should return when Outlook reconnects. However, a contact or other item stored only locally may not. Check the account’s online view and distinguish OST files from PST archives before changing anything.

Is an OST file the same as a PST file?
No. An OST is generally an offline working copy associated with an account that synchronizes with a server. A PST can store mail and other Outlook data locally, including archives. Treat a PST as potentially important data, not as a cache to discard.

Can I clear Outlook cache without closing the app?
You can clear Auto-Complete from Outlook’s options while it is running. For an OST rebuild, close classic Outlook first so the file is not in use. For new Outlook, use Windows’ app repair or reset controls rather than manually removing an OST.

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