Clear Outlook Cache on Mac Without Losing Local Mail

Outlook on a Mac has more than one kind of cache. Clearing temporary app files is a different operation from resetting a mail account, and neither justifies deleting the Office folder that holds your Outlook profile. Start by deciding whether you need to fix missing mail or reduce disk usage, then change only the data involved.

Separate App Cache From Mail Data

There are two locations worth distinguishing:

• ~/Library/Caches/com.microsoft.Outlook is the app-cache path listed by Mole Mac. Check whether it exists on your installation, since an absent folder is not a fault.
• ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles is the profile location Microsoft documents for Outlook 2016 for Mac in its local-cache explanation. The page also applies to Microsoft 365 for Mac, but is not a complete map of every new Outlook build.

The second location contains mail-profile data, not a disposable temporary folder. Keep the parent ~/Library/Group Containers/UBF8T346G9.Office intact. Do not delete a profile, its database, or attachment files to imitate an in-app reset. Account configuration, local mail and settings need different handling from rebuildable app files, even when a storage tool shows them under the same Microsoft name.

Downloaded mail and attachments are offline copies only when a retrievable server copy exists. Microsoft's On My Computer documentation explains that local folders do not synchronize with a mail server, and POP mail can be stored there. An Exchange account does not make a separately saved local folder recoverable from Exchange.

Choose the Smallest Useful Change

Before any reset, open webmail for the same account and check several recent messages and important older attachments. Check drafts, outgoing mail and locally stored folders separately. Seeing the inbox online does not prove that every item on the Mac has synchronized. If you cannot establish which copy is authoritative, stop before clearing mail data.

Use Outlook's Own Repair Control First

New Outlook: Reset the Affected Account

Microsoft's account-cache instructions give this route: Tools › Accounts, select the affected account, then Manage › Reset Account. Stay connected to the server. Use this account-level route in new Outlook when these controls are available, rather than looking for a legacy folder dialog.

Microsoft explicitly warns that information not synchronized with the server will be deleted. Preserve local work first and reset only the affected account, then let synchronization finish before judging the result. This is a repair step for incomplete or incorrect server data, not a routine way to keep Outlook small. If your build does not show these controls, do not substitute a Finder deletion of the profile.

Legacy Outlook: Empty One Exchange Folder's Cache

For legacy Outlook, Microsoft's folder-cache instructions describe a narrower operation. While connected to Exchange, Control-click or right-click the affected Exchange folder in the navigation pane, choose Properties, then General › Empty Cache. Outlook downloads that folder's items from Exchange again.

This procedure also removes information that has not synchronized, including contacts' mail certificates according to Microsoft. Back up first. It applies to an Exchange folder, not a POP mailbox or any arbitrary local folder. The account reset and folder reset are separate documented interfaces, so a missing Empty Cache button does not mean you should delete files inside the Office group container.

Clear the App Cache by Hand With Outlook Quit

If synchronization works and the target is temporary app data, measure the cache before touching it. In Finder, press Shift + Command + G and paste:

~/Library/Caches/com.microsoft.Outlook

If the folder exists, inspect its size with Finder's Get Info. Record available disk space too. If it is small, clearing it cannot explain or resolve a much larger profile footprint. If it is missing, leave other Microsoft folders alone instead of guessing an equivalent path.

Quit Outlook completely before moving anything. Reopen the exact folder above, review its contents and move only those cache contents to the Trash. Leave the Office group container, Outlook's application container, preferences and account data alone. Keep the Trash for the first restart so the moved files remain recoverable, then reopen Outlook and check mail and attachments. This limited step does not reset a mailbox or reduce the amount of server mail Outlook needs to cache.

Only after checking the result should you empty the reviewed items from the Trash to release their disk space. Files still in the Trash still occupy storage. Recovery from the Trash is available only while those files remain there, and it is not a backup for local mail.

Check What Changed and Handle Failures

Test the original symptom, not just whether Outlook opens. Check the affected folder, send and receive a test message, open an older attachment and confirm any local folders are still present. Compare the same cache location and available space after synchronization settles.

Space did not come back: check whether the moved cache is still in the Trash, whether it was large enough to matter, and whether the large folder was actually the profile. Keep a large profile intact. Repeating account resets makes Outlook fetch its server copy again instead of removing the need for that copy.

Outlook downloads everything again: this is expected after the documented Exchange cache reset. Allow the first synchronization to finish. Cache growth during normal use is not by itself corruption, and repeated clearing can cost bandwidth without providing lasting free space.

You lost sign-in or local mail: stop deleting folders. Confirm you opened the correct account, retain anything still in the Trash, and use your backup or Microsoft support if local data is missing. Do not run another reset to try to recover unsynchronized items the first reset discarded.

Protect Local Mail and Know Where Mole Fits

Microsoft documents exporting an .olm archive in legacy Outlook. Use an export method supported by your installed version and verify that the archive can be imported before removing any original local mail. Do not assume a legacy export command exists in new Outlook. Without a working recovery method, keep the original profile. The Microsoft Office guide covers the separate case of removing Office, including the same warning about shared Outlook data.

Mole Mac's Clean lists ~/Library/Caches/com.microsoft.Outlook when it exists, has measurable content and passes its safety checks. It normally starts ticked when Outlook is closed and the item is eligible, rather than being review-only. User exclusions can hide it, and a running owner keeps it unselected. For this cache, Delete permanently is the default removal mode, while Move to Trash keeps it recoverable until the Trash is emptied. Clean protects the Office group-container profile and does not perform Outlook's account or Exchange-folder reset.

FAQ

Does Clearing Outlook Cache Delete My Emails?

Moving only the temporary app-cache contents is different from clearing account data. Microsoft's account and Exchange-folder resets discard unsynchronized information, and POP or On My Computer items may have no server copy. Verify and back up local data before any reset.

Can I Delete UBF8T346G9.Office to Get More Space?

Keep it while using Office. It holds shared data, including Outlook profiles, and is not an Outlook cache-cleaning shortcut. A smaller app cache does not make the profile disposable.

Why Does the Cache Grow Back?

Outlook needs local data to display server mail and attachments. A reset fetches that data again, so judge it by restored synchronization rather than lasting disk savings. Keep local-mail decisions separate from temporary-cache cleanup.