What clearing Outlook cache does and why you might need to

Clearing your Outlook cache removes temporary files, offline copies of emails, and stored data that Outlook keeps on your computer to speed up performance. Over time, this cache can grow large enough to slow down the program, cause it to freeze, or prevent new emails from syncing properly. Clearing it is safe — Outlook will rebuild the cache automatically the next time you open the program.

You might notice you need to clear cache if Outlook takes a long time to load, searches run slowly, or you see sync errors with your email account. The cache is separate from your actual emails, so clearing it will not delete any messages, contacts, or calendar events.

Key Takeaways

  • Outlook cache lives in different folders depending on whether you use Outlook desktop, Outlook on the web, or Outlook for Mac.
  • The fastest method for Outlook desktop is to use the built-in repair tool, which clears cache without manual file deletion.
  • If you manually delete cache files, you must close Outlook completely first or the files will not fully clear.
  • Clearing cache on Outlook for Mac requires navigating to the Library folder, which is hidden by default.

Clearing cache in Outlook desktop (Windows)

The easiest way to clear Outlook cache on Windows is through the built-in repair tool. Close Outlook completely, then open Control Panel and go to Programs > Programs and Features. Find Microsoft Office in the list, click it, and select Change. Choose Quick Repair first — this runs a fast check and often solves cache problems without needing a full repair.

If Quick Repair does not work, run it again and choose Online Repair instead. This process takes longer but clears more cache files and resets Outlook's connection to your email server. After either repair finishes, restart Outlook and it will rebuild the cache fresh.

If you prefer to delete cache files manually, close Outlook first. Open File Explorer and navigate to C:\Users\[YourUsername]\AppData\Local\Microsoft\Outlook. Look for files with the .ost extension — these are offline storage files that make up most of the cache. You can safely delete them. Outlook will recreate them the next time you open the program and sync with your email server.

Clearing cache in Outlook for Mac

Outlook for Mac stores cache in the Library folder, which is hidden by default. Close Outlook, then open Finder. Press Command + Shift + G to open the "Go to Folder" dialog, paste ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles, and press Enter. Inside this folder, look for a folder named after your email account.

Open that account folder and delete the Data folder — this contains the cache. Leave everything else in place. Restart Outlook and it will rebuild the cache as it syncs with your email server. The process may take several minutes depending on how many emails you have.

Clearing cache in Outlook on the web

Outlook on the web (the browser version) stores cache in your browser, not on Outlook's servers. To clear it, open your browser settings and find the option to clear browsing data or cache. In Chrome, this is Settings > Privacy and Security > Clear Browsing Data. In Edge, it is Settings > Privacy > Clear Browsing Data. In Firefox, it is Settings > Privacy & Security > Cookies and Site Data.

Make sure you select the time range "All time" and check the boxes for "Cookies and site data" and "Cached images and files." Then click Clear. After you clear the browser cache, sign out of Outlook on the web and sign back in. Your browser will rebuild the cache as you use Outlook.

What to do if Outlook still runs slowly after clearing cache

If clearing cache does not solve the problem, the issue may be something else. Check how many emails are in your Inbox — if you have more than 50,000 emails in a single folder, Outlook can slow down significantly. Consider moving older emails to an archive folder or creating additional folders to split the load.

Another common cause is too many add-ins running in the background. Open Outlook in Safe Mode by holding Ctrl while launching it. If Outlook runs normally in Safe Mode, an add-in is the problem. Go to File > Options > Trust Center > Trust Center Settings > Disabled Items to see which add-ins are causing trouble, then disable them one at a time to find the culprit.

How often you should clear Outlook cache

Most users do not need to clear Outlook cache regularly. Clear it only when you notice performance problems or when troubleshooting a sync issue. If you clear cache frequently without a specific reason, you may actually slow Outlook down because it has to rebuild the cache more often.

If you find yourself clearing cache more than once a month, the underlying problem is probably not the cache itself. In that case, check your email account settings, make sure your internet connection is stable, and consider whether you need to archive old emails to reduce the total size of your mailbox.

Frequently Asked Questions

Will clearing cache delete my emails?

No. Cache is temporary data Outlook uses to run faster. Your actual emails, contacts, and calendar events are stored on your email server and in Outlook's main data files, which clearing cache does not touch. After you clear cache, Outlook will download your emails again the next time you open it.

How long does it take Outlook to rebuild cache after clearing it?

Rebuilding usually takes a few minutes for small mailboxes and up to 30 minutes for very large ones with thousands of emails. During this time, Outlook may run slowly or show a sync indicator. Let it finish before closing the program.

Can I clear cache without closing Outlook?

Not effectively. If Outlook is running, it will keep using the cache files and may recreate them as you work. Always close Outlook completely before clearing cache manually or running a repair.

What is the difference between Quick Repair and Online Repair?

Quick Repair checks Outlook's files and settings without connecting to your email server, and it takes a few seconds. Online Repair also reconnects to your server and resets your account settings, which takes several minutes but solves more problems. Try Quick Repair first.

Does clearing cache free up hard drive space?

Yes, sometimes significantly. Cache files can grow to several gigabytes over time, especially if you have a large mailbox. Clearing cache can free up 1 to 5 gigabytes depending on how long you have used Outlook without clearing it.