How to Clear the Cache in Outlook (And Why It Matters)

If Outlook has been acting sluggish, showing outdated email addresses in autocomplete, or displaying stale search results, the cache is often the culprit. Outlook stores temporary data locally to speed things up — but over time, that same data can cause more problems than it solves. Clearing it is one of the most effective first steps when troubleshooting common Outlook issues.

What Does Outlook Actually Cache?

Outlook maintains several different types of cached data, and they don't all live in the same place:

• Autocomplete cache — stores email addresses you've typed or used before, so Outlook can suggest them automatically
• Offline cached mail — a local copy of your mailbox stored in an OST file, allowing Outlook to work without a live connection
• Thumbnail and icon cache — cached images and interface assets that speed up rendering
• Suggested contacts — names and addresses Outlook learns from your sending habits

Each of these caches serves a different function, which means clearing them requires different steps — and not all of them should be cleared in every situation.

How to Clear the Autocomplete Cache in Outlook

The autocomplete cache is the most commonly problematic one. If Outlook keeps suggesting wrong or outdated email addresses, this is where to start.

In Outlook for Windows (classic desktop app):

1. Go to File → Options → Mail
2. Scroll down to the Send Messages section
3. Click Empty Auto-Complete List
4. Confirm when prompted

You can also delete individual suggestions on the fly — start typing a name in the To field, hover over the unwanted suggestion, and click the X that appears next to it.

In Outlook on the Web (OWA): The autocomplete list in the browser version is managed separately and resets based on your session and browser cache rather than a stored Outlook file.

How to Clear the Offline Cache (OST File)

The OST file is Outlook's local copy of your mailbox. When it becomes corrupted or bloated, you may see sync errors, missing emails, or slow performance. Clearing it forces Outlook to re-download a fresh copy from the server.

⚠️ Only do this if you're connected to Exchange, Microsoft 365, or an IMAP account — the data lives on the server and will re-sync. Don't do this with POP3 accounts, where the local file may be your only copy.

Steps for Windows:

1. Close Outlook completely
2. Open Control Panel → Mail → Email Accounts
3. Select your account and click Change
4. Under Offline Settings, reduce the cache slider or uncheck Use Cached Exchange Mode temporarily
5. Alternatively, locate the OST file (typically in C:Users[YourName]AppDataLocalMicrosoftOutlook) and delete or rename it
6. Reopen Outlook — it will rebuild the cache from the server

The rebuild process can take anywhere from a few minutes to several hours depending on mailbox size and connection speed.

How to Clear the Cache in Outlook for Mac

The Mac version handles caching differently from Windows.

1. Quit Outlook
2. Open Finder → Go → Go to Folder
3. Type: ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/
4. Locate your profile folder and look for the cache or data folder
5. Delete the contents (not the folder itself)
6. Relaunch Outlook

The exact folder path can vary slightly depending on which version of Outlook for Mac you're running (the Microsoft 365 version vs. older standalone versions).

How to Clear the Cache in the Outlook Mobile App

On iOS and Android, the simplest method is removing and re-adding your account:

1. Go to Settings (gear icon) within the Outlook app
2. Tap your account name
3. Select Delete Account
4. Re-add the account from scratch

On Android, you can also go to your device's Settings → Apps → Outlook → Storage → Clear Cache — this wipes temporary files without removing your account credentials.

Variables That Affect Your Approach 🔧

Not all cache-clearing situations are equal. A few factors shape which method is appropriate:

Someone using Outlook as part of a corporate Microsoft 365 environment on Windows will follow a completely different process than someone using the Outlook app on an iPhone with a personal Gmail account connected through IMAP.

When Clearing the Cache Doesn't Fix the Problem

If issues persist after clearing the relevant cache, the problem may lie elsewhere — a corrupted Outlook profile, a server-side sync issue, outdated software, or a conflict with another application. In those cases, clearing the cache was still a valid first step, but the root cause sits in a different layer of the system.

Your specific setup — account type, platform, Outlook version, and what's actually going wrong — determines which cache to target and whether clearing it alone will be enough to resolve what you're seeing. 🗂️