Clear Outlook Cache: Safe Steps and What They Remove

Yes—clear an Outlook cache when it is causing a specific problem, but first identify which cache you mean. For classic Outlook on Windows, you can clear saved address suggestions at File > Options > Mail > Empty Auto-Complete List; rebuilding an offline mailbox cache is a different, more disruptive step.

“Outlook cache” can refer to several kinds of locally stored information, and deleting the wrong item can remove data you still need. The safest approach is to choose the relevant cache, check that important changes are synchronized or backed up, and use Outlook or Windows settings where possible.

What Outlook’s local cache contains

Outlook keeps some information on your computer so it can open messages quickly, work when a connection is unavailable, and offer useful suggestions. The details depend on the Outlook version, account type, and feature involved. A cache is not necessarily a spare copy of every Outlook item: some local files are synchronized copies, while other data files may be the only place a message is stored.

Common meanings of “Outlook cache” include:

Offline mailbox cache: In classic Outlook, an OST file can hold a synchronized copy of an Exchange, Microsoft 365, Outlook.com, or other supported account’s mailbox for offline use.
Auto-Complete suggestions: Outlook can save addresses you have typed in the recipient fields. This is separate from the contacts in your address book.
New Outlook app data: The Windows app may retain local settings and data that can be repaired or reset through Windows app settings.
Temporary files: Outlook and Windows can use temporary storage for operations such as opening attachments. That is not the same as the mailbox cache.

Consequently, clearing one cache will not necessarily fix a problem caused by another. For example, removing a recipient suggestion will not refresh a mailbox that is failing to synchronize.

Choose the cache that matches the problem

Match the action to the symptom before you delete anything. If Outlook suggests an outdated or incorrect email address, clear or remove the Auto-Complete suggestion. If a classic Outlook mailbox displays stale content or synchronization errors, investigate the OST cache. If the new Outlook app is freezing or behaving incorrectly, try its repair option before resetting it.

Wrong address appears while composing: Remove that specific Auto-Complete entry or clear the whole list.
Mailbox folders are not updating in classic Outlook: Check connection and synchronization status first; rebuilding the OST may help if the local cache is damaged.
New Outlook will not open or repeatedly crashes: Try Windows’ Repair option, then consider Reset if Repair does not help.
An attachment will not open: Check the file, permissions, security settings, and available disk space before assuming the mailbox cache is the cause.

Clearing caches is not a general-purpose way to make an Outlook account faster. A large mailbox can take time to download again after an OST rebuild, and the same information may return as Outlook synchronizes.

Clear Auto-Complete suggestions in classic Outlook

Auto-Complete is the list of suggested recipients that appears as you type in the To, Cc, or Bcc field. It is not your Contacts folder, and clearing it does not delete those contacts or messages. In classic Outlook for Microsoft 365 on Windows, use these steps:

Open Outlook and select File > Options.
Select Mail.
Under Send messages, select Empty Auto-Complete List.
Confirm the action when Outlook asks.

This clears the saved suggestions as a group. Outlook can build the list again as you address new messages. To remove only one incorrect suggestion, start a new message, type enough of the address or name to show the suggestion, and select the remove control beside that entry if it appears. Removing an entry this way does not delete a matching contact from your address book.

On Mac, Outlook’s controls and labels differ by version, and the Windows File > Options path does not apply. In new Outlook for Windows, use the remove control beside an individual suggestion when it is displayed; do not assume the classic Outlook option for emptying the entire list is present. If you cannot find an equivalent control, check Outlook’s current settings and help for your installed version rather than deleting unrelated files.

Rebuild the offline mailbox cache in classic Outlook

For a synchronized account, classic Outlook’s OST file is a local offline copy. Rebuilding it makes Outlook create a fresh file and download mailbox content again. This can resolve some problems caused by a damaged local cache, but it is not the first troubleshooting step: a slow connection, a service outage, an account issue, or a large mailbox can produce similar symptoms.

Before proceeding, connect to the internet and check that Outlook has synchronized recent changes. Look for an up-to-date status in Outlook, and confirm that important sent messages, drafts, calendar changes, and contacts are visible in Outlook on the web or another trusted view of the account. If you have work that exists only locally, save or copy it before rebuilding. Do not treat a POP account’s PST file as a disposable cache; it may contain the only copy of local mail.

Close Outlook completely. If it is still running in the background, wait for it to exit before handling the data file.
In classic Outlook, open File > Account Settings > Account Settings, then select the Data Files tab. Select the relevant file and choose Open File Location, if available.
Identify the OST belonging to the account you intend to refresh. Do not select or rename a PST file. If you are unsure which file is which, stop and ask your organization’s support team.
Rename the OST, for example by adding .old to its name, rather than permanently deleting it immediately. Windows may require you to change the extension only after confirming that file extensions are visible.
Open Outlook again. It should create a new cache for the account and synchronize available mailbox content. Keep the computer connected and allow time for the download to finish.

Renaming instead of immediately deleting gives you a short-term fallback, but an old OST is not a substitute for a proper backup and may not be reusable. Once you have confirmed the new cache works and the required information is available, you can remove the old file to reclaim disk space. If Outlook does not recreate the file, asks for unexpected credentials, or shows missing items, stop rather than deleting more files.

Repair or reset new Outlook for Windows

New Outlook for Windows is a separate app experience from classic Outlook, so classic Outlook’s OST instructions and ribbon options may not apply. If the app is malfunctioning, Windows provides app troubleshooting options. In Windows 11, open Settings > Apps > Installed apps, locate Outlook (new), select the three-dot menu, and choose Advanced options if that option is available.

Choose Repair first. Repair is intended to address app problems without the broader effect of resetting the app. If the issue continues, Reset may clear local app data and settings and can require you to set up or sign in to accounts again. The exact labels and availability can vary with the Windows and Outlook versions managed on your device.

Before resetting, make sure you know how to sign in again and that important mail and calendar data is available through the account’s server or another backup. A reset is not the same as deleting an account from the mail service, but it can remove information kept only in the app. For a work or school device, check with your administrator before resetting if the app is managed by your organization.

What clearing the cache does—and does not do

For a properly synchronized Microsoft 365 or Exchange mailbox, rebuilding the OST normally causes Outlook to download a fresh local copy from the server. It does not, by itself, delete the server mailbox. However, that reassurance depends on the account and on synchronization being complete. It is not safe to assume that everything is on the server just because it appears in Outlook.

Clearing the Auto-Complete list removes suggested recipients, not contacts. Repairing or resetting new Outlook affects the app’s local state, not the account itself. Deleting a PST, removing an account, or deleting files from an unfamiliar Outlook folder can have much more serious consequences. If you use a POP account, archive mail locally, or have unsent work, verify where that information is stored before taking action.

Also expect a rebuilt mailbox cache to use disk space again and take time to populate. During synchronization, search results may be incomplete, older mail may appear gradually, and offline access may be limited until the download finishes. Leave Outlook open and connected if your organization’s policies allow it, and avoid interrupting the initial sync unless Outlook reports an error.

Common problems and safer alternatives

A cache reset may not solve the underlying cause. Before rebuilding an OST or resetting the app, try lower-risk checks that fit the problem:

Confirm that the computer has an internet connection and that Outlook is not set to work offline.
Check whether Outlook on the web shows the same missing or outdated messages. If it does, the issue may be account-side rather than a local cache problem.
Restart Outlook and Windows, then check whether the issue remains.
Install available Office or Windows updates if your organization permits updates.
For recipient suggestions, remove only the incorrect suggestion instead of clearing every saved suggestion.
For new Outlook, use Repair before Reset. For a managed work account, ask IT whether an outage or policy is affecting synchronization.

If Outlook reports that a data file cannot be accessed, do not delete files at random or create a new profile as a first response. Confirm the account type and the file extension, then follow Microsoft’s support guidance or contact your administrator. A profile rebuild can be useful in some cases, but it is a different troubleshooting action from clearing a cache and can require account setup again.

Frequently Asked Questions

Will clearing the Outlook cache delete my emails?
Clearing Auto-Complete suggestions does not delete email. Rebuilding the OST for a synchronized account normally refreshes its local copy from the server, but first confirm that recent changes are synchronized. A PST can hold mail stored only on the computer, so do not delete it as if it were a cache.

How do I clear Outlook’s cache without deleting contacts?
In classic Outlook for Windows, File > Options > Mail > Empty Auto-Complete List clears recipient suggestions, not the Contacts folder. To preserve other suggestions, remove only the incorrect entry using its remove control when it appears in the recipient suggestions.

Should I delete the OST file?
Only consider rebuilding an OST when you have a specific synchronization or cache problem and have checked that important changes are synchronized. Close Outlook first, identify the correct OST, and rename it rather than immediately deleting it. Never confuse it with a PST.

Why is Outlook slow after I clear its cache?
A rebuilt cache has to download mailbox data again. Until synchronization finishes, Outlook may use more network and disk resources, and some offline content or search results may be incomplete. If slowness persists after synchronization, investigate other causes such as connection quality, mailbox size, add-ins, or an account or service problem.

Does clearing the cache fix Outlook synchronization errors?
Sometimes rebuilding a damaged local cache helps, but it cannot fix every sync problem. Check the internet connection and whether the same issue appears in Outlook on the web. If the problem affects multiple devices or persists after a rebuild, contact your email administrator or Microsoft support.

Try it: the Date Difference Calculator: days, months, years and weekdays between two dates, with the DATEDIF formulas.

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