Clear Cache in Outlook for Windows 10: Step-by-Step

To clear cache in classic Outlook on Windows 10, first choose which cache is causing the problem: use File > Options > Mail > Empty Auto-Complete List for remembered addresses, or close Outlook and rebuild its offline data file if mail is stuck or out of date. Outlook has several separate caches, so there is no single safe button that clears them all. Before changing offline data, make sure your mailbox is connected and synchronized.

What You’ll Need

A Windows 10 PC with classic Outlook for Microsoft 365, Outlook 2021, or a similar desktop version installed. These steps do not apply exactly to the newer Outlook app.
A few minutes with Outlook closed for the file-based options. Save open messages and attachments first.
If you plan to rebuild an offline data file, a working internet connection and access to your Microsoft 365, Exchange, or email account so Outlook can download the mailbox again.

Step-by-Step

Identify the issue and choose the matching cache. If Outlook suggests an old or incorrect recipient, clear the Auto-Complete list in step 2. If email is missing, stale, or not syncing in a Microsoft 365 or Exchange account, consider rebuilding the offline Outlook data file in step 5. If an attachment preview or temporary attachment is behaving oddly, use step 6. You usually do not need to perform every option.
Clear the full Auto-Complete list, if that is the problem. In classic Outlook, select File > Options > Mail. Under the Send messages section, select Empty Auto-Complete List, then confirm. Close and reopen Outlook and start a new message to check the result. This removes the remembered recipient suggestions; it does not delete contacts from your address book or remove messages.
Remove just one incorrect recipient suggestion instead. Start a new email and type enough of the address or name to show the suggestion. Select the unwanted entry and use the small X beside it if shown. In some Outlook versions, you can highlight the suggestion with the arrow keys and press Delete. This is preferable to emptying the whole list when only one address is wrong. Do not press Delete while the recipient is already in the To field unless you intend to remove that recipient from the message.
Restart Outlook and check whether the change worked. Close all Outlook windows, wait a few seconds, and open Outlook again. For an Auto-Complete issue, compose a test message and type the recipient’s name. For a sync issue, check the status bar at the bottom of Outlook for a connected or up-to-date message, then send or receive a small test message if appropriate.
Rebuild an Exchange or Microsoft 365 offline data file only if needed. This file, with an .ost extension, keeps a local synchronized copy of mailbox data so Outlook can work offline. In Outlook, open File > Account Settings > Account Settings, select the Data Files tab, select the relevant account or data file, and choose Open File Location. Note the file name and location. Close Outlook completely, including any Outlook icon still running in the notification area. In File Explorer, rename the relevant .ost file, for example by adding .old to its name. Do not rename a .pst file. Reopen Outlook while connected to the internet; Outlook should create a fresh .ost and synchronize the mailbox. Initial downloading can take time, especially for a large mailbox.
Confirm that your data is safe before rebuilding. An .ost is normally a synchronized copy of server-held mail, calendar, and contacts, but do not assume every item has reached the server. Before renaming it, check that Outlook is online and has finished synchronizing, and verify that recent messages appear in Outlook on the web or another connected device. If Outlook is the only place an unsent message or recent change exists, do not rebuild the file until you have resolved that. If you cannot identify the correct file, ask your organization’s IT support rather than deleting files at random.
Clear temporary attachment files if previews or cached attachments are the issue. Save your work and exit Outlook. Press Windows key + R, enter %LOCALAPPDATA%\Microsoft\Windows\INetCache\Content.Outlook, and press Enter. If the folder opens, remove its contents, not the Content.Outlook folder itself. Windows may ask for administrator permission or report that a file is in use; skip that file rather than forcing it. These are temporary attachment copies, not the original attachments in your mailbox. If the folder does not exist, skip this step; its location can vary by Outlook version and configuration.
Clear the custom forms cache only when a form is malfunctioning. In classic Outlook, go to File > Options > Advanced, find the Custom Forms area, and select Custom Forms or Manage Forms, depending on the version. In the Forms Manager, choose Clear Cache if available. This affects cached Outlook forms, not mail or contacts. If you do not use custom forms or cannot find that control, leave it alone.
Test Outlook before making more changes. Reopen Outlook, allow it to finish connecting or synchronizing, and repeat the action that was failing. If you rebuilt an .ost, keep Outlook open and connected while the mailbox repopulates. Avoid repeatedly clearing caches during the download because it can make diagnosis harder and may prolong the process.

Common Mistakes

Deleting the wrong file. An .ost is an offline copy associated with certain account types; a .pst can contain locally stored or archived mail. Do not delete or rename a .pst as a cache-clearing shortcut. If you are unsure which file Outlook uses, stop and ask for help.
Assuming clearing Auto-Complete deletes contacts. It removes suggested recipients only. Contacts saved in People or the Contacts folder are separate.
Clearing every cache for a small problem. Choose the narrowest relevant fix. Emptying all suggestions, rebuilding a mailbox file, and clearing attachment files are different actions with different effects.
Rebuilding an offline file while Outlook is disconnected. Recent changes may not have synchronized. Confirm the mailbox is online and current first, particularly before renaming an .ost.
Deleting files while Outlook is open. Outlook may recreate or lock them, and attachment files could still be in use. Close Outlook first and skip locked files.
Applying classic Outlook instructions to the new Outlook app. The newer app does not use the same local .ost workflow or classic ribbon paths. Identify which Outlook you have before following file-based steps.

Tips

Start with the symptom. Wrong address suggestions point to Auto-Complete; an attachment preview problem points to temporary attachment files; a mailbox that will not update may need a sync check before considering an .ost rebuild.
Keep a note of what you changed. If you rename an .ost file, record its original name and location. Renaming instead of deleting gives you a chance to restore it if you later discover you selected the wrong file. Do not restore an old file over a newly synchronized one without advice.
Allow time for the first synchronization. A rebuilt offline file may take minutes or longer to download, depending on mailbox size, connection speed, and organization settings. Outlook can appear slower while this happens.
Use Outlook on the web as a useful comparison. If a message is present online but missing in desktop Outlook, the issue may be with local synchronization. If it is missing in both places, clearing the desktop cache is unlikely to bring it back.
Know the Mac difference. These Windows paths and ribbon instructions are for classic Outlook on Windows. Outlook for Mac manages its local data differently; do not try to use Windows cache folders on a Mac. In new Outlook for Windows, use its available app repair or reset controls only if necessary, and expect to sign in and let the app resynchronize.

Troubleshooting

Empty Auto-Complete List is missing or unavailable: Check that you are using classic Outlook and that you opened File > Options > Mail, not Outlook on the web or the new Outlook app. You can remove individual suggestions by starting a message and selecting the X beside the unwanted result. If your organization manages Outlook settings, an administrator may have disabled or altered the control.

The .ost file is not listed or Open File Location does not work: Some accounts do not use an .ost file, and the Data Files tab may show different entries depending on account setup. Do not search the whole drive and rename a file based on its name alone. Check the account type in Account Settings. If this is a POP account or you see a .pst file, get help before changing local data; a .pst may be the only copy of older messages.

Outlook does not recreate the .ost or keeps showing old data: Confirm that Outlook is online, the account password is accepted, and there is enough free disk space. Check the status bar for a synchronization message and leave Outlook open. If it reports a specific connection or sign-in error, fix that first; clearing cache cannot repair a blocked account or network connection. On a work account, contact IT if the mailbox is managed by your organization.

The attachment cache folder is missing or files cannot be removed: The folder may not have been created on this PC, or Outlook may use a different location. Skip the step if the path does not open. If a file is locked, close the program using the attachment and try again later; do not force-delete it. The original message attachment remains in the mailbox unless you separately delete the message.

You use new Outlook for Windows: The classic File > Options menus and the .ost instructions may not apply. In Windows 10, open Settings > Apps > Apps & features, select Outlook (new), and choose Advanced options if it is offered. Try Repair first; use Reset only if needed, since it can clear local app data and require you to sign in again. Menu availability varies with the app version. If the issue remains, update the app or contact support.

Frequently Asked Questions

Does clearing Outlook cache delete my email?
Clearing the Auto-Complete list does not delete email. Temporary attachment files are local copies. Rebuilding an .ost normally makes Outlook download a fresh copy of synchronized mailbox data, but verify synchronization first and do not treat a .pst as disposable cache.

How often should I clear Outlook cache?
There is no routine schedule. Clear a specific cache when you have a related problem, such as a wrong recipient suggestion or a broken attachment preview. An .ost rebuild is a troubleshooting step, not regular maintenance.

Will clearing cache make Outlook faster?
It may help if a damaged local cache is causing a particular fault, but it is not a general speed boost. Large mailboxes, add-ins, network issues, low disk space, and account problems can also affect performance. A fresh .ost may temporarily make Outlook slower while it downloads data.

Can I clear only one remembered email address?
Yes. Start a new message, type the name or address, and remove the unwanted suggestion using its X or, in some versions, by selecting it with the arrow keys and pressing Delete. This leaves other Auto-Complete suggestions in place.

What is the difference between an .ost and a .pst?
An .ost is generally a local offline copy for a mailbox that synchronizes with a server. A .pst is a separate Outlook data file often used for POP mail, archives, or exported data. A .pst may hold the only copy of some messages, so never delete it just to clear cache.

Do these steps work in Outlook for Mac?
No. The Windows folders and menu paths in this guide are for classic Outlook on Windows 10. Outlook for Mac has different account and data-management controls; use Mac-specific support instructions rather than changing Windows files.

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