What clearing Outlook cache does and why you might need to

Clearing your Outlook cache removes temporary files that Outlook stores on your computer — things like downloaded email attachments, message previews, and search indexes. Over time, this cache can grow to several gigabytes and slow down Outlook's performance, cause sync problems between your device and the mail server, or prevent you from opening certain emails.

You do not lose any actual emails or contacts when you clear the cache. Outlook will re-download what it needs the next time you open it. The process takes between five and thirty minutes depending on how much cache has built up and which method you use.

The most common reasons to clear cache are: Outlook is running slowly, you are seeing repeated error messages, you want to reclaim disk space, or you are troubleshooting a sync problem with your email account.

Key Takeaways

  • Clearing Outlook cache removes temporary files but keeps all your actual emails, contacts, and calendar events intact.
  • The fastest method is to close Outlook completely, delete the cache folder manually, and restart the program.
  • On Windows, the cache folder is usually at C:\Users\[YourUsername]\AppData\Local\Microsoft\Outlook.
  • On Mac, the cache folder is in ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles.
  • If you are not comfortable deleting files manually, Outlook's built-in settings can clear cache automatically over time.

Clearing cache on Windows

The manual method is fastest. Close Outlook completely — check your taskbar to make sure no Outlook window is running. Then open File Explorer and navigate to C:\Users\[YourUsername]\AppData\Local\Microsoft\Outlook, replacing [YourUsername] with your actual Windows username.

If you do not see the AppData folder, you need to show hidden files. In File Explorer, click the View tab at the top, then check the box next to "Hidden items". Now you can see AppData.

Inside the Outlook folder, you will see several files and subfolders. Delete everything except Outlook.xml and any folder named with your email address (for example, user@example.com). These contain your account settings and should be left alone. Select all the other files and folders, press Delete, and confirm.

Restart Outlook. It will rebuild the cache as you use it. The first time you open it after clearing cache, it may take longer than usual to load.

Clearing cache on Mac

Close Outlook completely. Open Finder and press Command+Shift+G to open the "Go to Folder" dialog. Paste this path: ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles

You will see one or more folders with names like "Main Profile" or your email address. Open the folder that corresponds to the Outlook account you want to clear cache for. Inside, look for a folder called Data or Cache. Delete the contents of that folder, but leave the folder itself in place.

If you see a file called Outlook Offline Address Book or Offline Address Book, you can delete that too — it will be rebuilt when you restart Outlook. Restart Outlook and let it rebuild the cache.

Using Outlook settings to clear cache automatically

If you prefer not to delete files manually, Outlook has a built-in option to reduce cache size. Open Outlook and go to File > Options (Windows) or Outlook > Preferences (Mac). Look for the section labeled "Advanced" or "Storage".

On Windows, click File > Options > Advanced, then scroll down to find "Offline Settings" or "Cached Exchange Mode". You can adjust how much email Outlook keeps cached locally — reducing this number will free up space over time, though Outlook will need to download more from the server when you switch between folders.

On Mac, go to Outlook > Preferences > General, then look for "Offline Settings". You can set Outlook to keep only the past 30 days of email cached instead of everything, which reduces cache size significantly.

When to clear cache versus when to rebuild it

Clearing cache is a simple delete-and-rebuild process. Rebuilding cache is different — it means asking Outlook to re-index all your emails and rebuild its search database. You only need to rebuild cache if you are having search problems or if Outlook is showing you incorrect message counts.

To rebuild cache on Windows, go to File > Options > Advanced > Outlook Data Files, select your account, and click "Rebuild". On Mac, go to Tools > Rebuild Outlook Data File. This process can take an hour or more if you have thousands of emails, so start it when you do not need to use Outlook.

For most performance problems, a simple cache clear is enough. Only rebuild if clearing cache did not solve the problem.

What to do if Outlook will not start after clearing cache

If Outlook fails to start after you clear the cache, you may have accidentally deleted a file that Outlook needs. The safest fix is to restart your computer, then open Outlook. Outlook will detect that some files are missing and will rebuild them automatically.

If that does not work, you can restore the cache folder from your computer's recycle bin (Windows) or trash (Mac). Open the recycle bin or trash, find the Outlook folder, and restore it. Then try opening Outlook again.

If Outlook still will not start, try repairing the Office installation. On Windows, go to Control Panel > Programs > Programs and Features, find Microsoft Office, click it, and select "Change". Choose "Quick Repair" first; if that does not work, run "Online Repair". On Mac, uninstall Outlook completely and reinstall it from the Microsoft Office website or the App Store.

How much space clearing cache actually frees up

The amount of space you recover depends on how long you have been using Outlook and how many emails you have. A typical cache folder is between 500 megabytes and 3 gigabytes. If you have been using Outlook for several years without clearing cache, you might recover 5 gigabytes or more.

To see how much space your cache is using before you clear it, right-click the Outlook folder (Windows) or select it and press Command+I (Mac) to view its size. After you clear it and restart Outlook, check the size again after a few hours — you will see it has grown back, but usually not to the original size because Outlook is more selective about what it caches on the second pass.

Frequently Asked Questions

Will clearing cache delete my emails?

No. Your actual emails stay on the mail server and in your Outlook mailbox. Clearing cache only removes temporary copies that Outlook downloaded. When you restart Outlook, it will download them again.

How often should I clear Outlook cache?

Most people do not need to clear cache more than once or twice a year unless they are experiencing performance problems. If you notice Outlook slowing down or sync errors happening regularly, clearing cache every few months may help.

Can I clear cache while Outlook is running?

No. Outlook locks the cache files while it is open, so you cannot delete them. You must close Outlook completely before clearing cache manually. If you use the built-in settings method, Outlook can clear cache in the background without closing.

What is the difference between clearing cache and clearing search history?

Cache is temporary files Outlook stores on your computer. Search history is the list of searches you have performed in Outlook. Clearing cache does not clear search history, and clearing search history does not clear cache. To clear search history, go to File > Options > Advanced and look for "Search" options.

Does clearing cache affect my contacts or calendar?

No. Contacts and calendar events are stored separately from cache. Clearing cache will not remove or change any contacts, calendar entries, or tasks. They will still be there when you restart Outlook.