How to Clear Cache in Outlook for Windows

To clear Outlook’s local cache in Windows, first identify which Outlook you use: in classic Outlook, clear the Auto-Complete list or rebuild the account’s OST file; in new Outlook, use Windows’ Reset option. These actions address different kinds of cached data, so choose the one that matches the problem. Your mail stored on the account’s server normally remains there, but unsent or unsynchronized changes may not.

Before starting, make sure Outlook is connected to the internet and allow it to finish sending and receiving mail. A cache is a local copy or temporary record that can help Outlook work faster, including when you are offline. Clearing it can fix display, search, or synchronization problems, but Outlook may take time to download messages and attachments again. Do not delete a PST file: it can contain the only copy of locally stored mail.

What You’ll Need

A Windows PC with Outlook installed and permission to close and reopen the app.
Your Microsoft 365, Exchange, or other mail account credentials, in case Outlook asks you to sign in again.
A few minutes for the mailbox to synchronize afterward. A large mailbox or slow connection may need considerably longer.
If you plan to rebuild a cache file, confirmation that important mail and changes have synchronized to the server. If you are unsure, do not delete files; start with the Auto-Complete option or ask your organization’s IT support.

Step-by-Step

Check whether you have classic Outlook or new Outlook. Classic Outlook has a File tab in its main window and a traditional ribbon. New Outlook has a redesigned interface and generally does not have that same File > Options path. If you are unsure, search for Outlook in the Windows Start menu; the app may be labelled Outlook (new). The methods below are separated because their cache controls differ.
Save work and let Outlook synchronize. In Outlook, choose Send/Receive > Send/Receive All Folders if that command is available, and wait for any sending or syncing activity to finish. Check the Outbox for messages waiting to send. If you have edited drafts or other items while offline, reconnect and confirm they appear in your mailbox before rebuilding a cache. Do not proceed with an OST rebuild if you cannot confirm that important changes are synchronized.
For classic Outlook, clear the Auto-Complete cache if address suggestions are the problem. This is the least disruptive option and removes remembered recipient suggestions; it does not clear downloaded mail or attachments. Select File > Options > Mail. Under Send messages, select Empty Auto-Complete List, then confirm. Close and reopen Outlook. Recipient suggestions will be collected again as you address new messages. If you only need to remove one incorrect suggestion, start a new message, type enough of the address to show the suggestion, then select the X beside that entry rather than emptying the entire list.
For a mailbox synchronization or display problem, identify whether the account uses an OST. In classic Outlook, select File > Account Settings > Account Settings, then open the Data Files tab. Look for the data file associated with the account and its file type or location. An OST is an offline cache used by supported Exchange, Microsoft 365, and IMAP configurations. A PST is a personal data file that may hold locally stored mail, especially with a POP account. If the file is a PST, stop here: do not delete it to clear a cache.
Open the OST’s folder, then close Outlook completely. In the Data Files tab, select the relevant OST and choose Open File Location if that button is available. Note the folder and file name. Close Outlook, then check that it has exited; if necessary, wait a moment and verify in Task Manager that OUTLOOK.EXE is no longer running. Do not remove a file while Outlook is open. If you cannot confidently identify the correct OST, cancel rather than guessing.
Rename the OST instead of permanently deleting it. In File Explorer, locate the specific .ost file and change its name, for example by adding .old to the end. Windows may warn that changing a file extension could make it unusable; confirm only if you have verified it is the OST you intend to rebuild. Renaming keeps a fallback copy. Do not rename or delete other Outlook files, and do not apply this procedure to a PST.
Restart classic Outlook and let the cache rebuild. Open Outlook and sign in if prompted. Outlook should create a new OST and download the mailbox again. Keep the computer online and, if possible, prevent it from sleeping during the initial synchronization. Messages and folders may appear gradually; search results, shared mailboxes, and older mail can take longer. Avoid repeating the rename while the first synchronization is still underway.
For new Outlook, reset the app only if its local data needs to be refreshed. Close Outlook. In Windows, open Settings > Apps > Installed apps, find Outlook (new) or Outlook, select the three-dot menu, and choose Advanced options. If the page provides a Repair option, try that first because it is less disruptive. If Repair does not help, select Reset and confirm. Reset can remove local app data and sign you out, so make sure you know your account password and can complete any multifactor sign-in. Open Outlook again and add or sign in to the account if asked; allow it to synchronize. This Windows reset is different from clearing an OST in classic Outlook.
Check the result before removing any backup. Confirm that the affected account is connected, folders and recent messages appear, and the original issue has improved. If you renamed an OST, keep the .old file temporarily until you are sure Outlook has rebuilt the cache and your expected mail is present. Do not import that renamed file or delete it immediately as a troubleshooting shortcut. If mail is missing, stop and investigate before removing the fallback.

Common Mistakes

Deleting a PST because it looks like a cache. A PST can store mail, calendar items, and contacts locally. Removing it may make those items inaccessible. Only consider rebuilding an OST that belongs to a server-backed account, and verify the file extension first.
Assuming every cache is the same. Clearing Auto-Complete removes address suggestions; rebuilding an OST refreshes an offline mailbox copy; resetting new Outlook refreshes app data. Choose the action that matches the symptom instead of doing all three.
Clearing the cache before offline work has synchronized. Unsynchronized changes, unsent messages, or local-only items may not be present on the server. Connect, send and receive, and check the Outbox and relevant folders first.
Removing files while Outlook is running. Outlook may still be using them, and Windows may block the action or the cache may not rebuild correctly. Close the app fully before working with an OST.
Expecting Outlook to be fast immediately. A rebuilt cache starts mostly empty. Mail, search indexes, and attachments may need to download or be generated again. A slow connection, large mailbox, or organization policy can extend the wait.
Using a file cleaner or deleting the entire Outlook folder. That can remove profiles or data files unrelated to the cache. Use the app’s own controls or work only with the specifically identified OST.

Tips

Start with the narrowest fix. If recipient suggestions are wrong, clear only Auto-Complete; there is no need to rebuild your mailbox cache.
Keep Outlook updated through the Microsoft 365 update options available to your organization. An outdated app can contribute to issues that clearing a cache will not fix.
After an OST rebuild, use Outlook normally while synchronization completes, but avoid repeatedly changing account settings or toggling cached mode. Those changes can complicate diagnosis.
If Outlook is managed by work or school, ask IT before resetting the app or renaming files. Policies, shared mailboxes, retention settings, and offline access may be centrally managed.
On a shared or public computer, do not leave a renamed cache file behind indefinitely. Once Outlook works and you have confirmed the mailbox is complete, ask your administrator whether it is safe to remove the old file.
On a Mac, Windows paths, the classic Outlook File > Options controls, and Windows app reset steps do not apply. Outlook for Mac has different settings and local storage; follow Mac-specific instructions rather than deleting Windows cache files.

Troubleshooting

Outlook will not reopen or says the data file cannot be found: Check that you renamed only the intended OST, not a PST or another account file. If Outlook cannot rebuild it, close Outlook and restore the original OST filename if you have not created new data since renaming. If the error continues, use the account repair options provided by your organization or contact support. Do not create a new profile or remove data files until you understand what they contain.

The mailbox looks empty after rebuilding: First check the connection indicator and confirm Outlook is signed in to the correct account. Allow time for synchronization, then check the mailbox in a browser or another trusted device. If the messages are present there but not in Outlook, the local download may still be in progress or the account may need attention. If the messages are absent everywhere, do not delete the renamed OST; contact your mail administrator or provider promptly.

Search results are incomplete: Give Outlook time to download content and rebuild its search index. Try searching for a recent, known message and confirm the correct mailbox and folder are included. If search remains incomplete after synchronization, follow Microsoft’s Windows search troubleshooting guidance or ask IT; repeatedly clearing the cache is unlikely to fix an indexing problem.

New Outlook has no Advanced options or Reset button: Windows labels and available controls can vary by release, installation type, and organizational policy. Search Windows Settings for Installed apps, select the Outlook entry, and check its app options. If Reset is unavailable, use any in-app sign-out and sign-in option your organization permits, or contact IT rather than removing app folders manually.

The old OST will not rename: Make sure Outlook and any background Outlook process are closed, then try again. A work device may restrict access to the folder; do not change permissions or use an unfamiliar cleanup tool to bypass that restriction. Ask an administrator for help.

The original issue returns after rebuilding: A cache rebuild addresses damaged or stale local data, not every cause of Outlook trouble. Check internet access, account status, available disk space, service outages, and whether the issue occurs in Outlook on the web. If it also occurs online, the cause is more likely account- or server-related than a Windows cache.

Frequently Asked Questions

Will clearing Outlook’s cache delete my emails?
Clearing Auto-Complete removes recipient suggestions, not messages. Rebuilding an OST normally downloads server-backed mail again, but unsynchronized changes and local-only content are at risk. A PST may contain the only copy of some items, so never delete it as a cache.

How do I clear Outlook’s cache without deleting emails?
For incorrect address suggestions in classic Outlook, use File > Options > Mail > Empty Auto-Complete List. For other problems, identify the account and file type before changing anything. Confirm server synchronization and avoid deleting PST files.

How long does an OST cache rebuild take?
It depends on mailbox size, connection speed, and organizational settings. Recent mail may appear before older content or attachments. Keep Outlook online and wait for synchronization to finish before deciding the rebuild failed.

Can I clear the cache in new Outlook using the classic Outlook steps?
No. New Outlook does not use the same classic File > Options controls or the same OST workflow for app reset. Use Windows Settings > Apps > Installed apps and the Outlook app’s Repair or Reset options when available.

Should I clear Outlook’s cache regularly?
Usually not. A cache helps Outlook work offline and load information more quickly. Clear or rebuild it when you have a specific symptom, and begin with a targeted action rather than routine deletion.

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