Understanding Outlook Cache and Why It Builds Up
Outlook, like most email programs, stores data on your computer to help it run faster. This stored data is called a cache. When you open emails, download attachments, or view images, Outlook saves copies of this information locally on your device. This caching system makes Outlook work more smoothly because the program doesn't have to fetch the same information repeatedly from the email server.
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Over time, your cache can grow quite large. A typical Outlook user might accumulate hundreds of megabytes or even gigabytes of cached data over several months or years. This happens naturally as you receive and open thousands of emails. The cache includes offline copies of your mailbox, temporary files from attachments you've opened, and copies of images that appear in emails you've viewed.
When your cache becomes very large, it can slow down your computer and cause Outlook to respond more slowly when you perform tasks like searching for emails, opening folders, or starting the program. Your computer's hard drive has to work harder to manage all this stored data. Additionally, a large cache can use up valuable storage space on your device, which might be particularly noticeable if you have a smaller hard drive or solid-state drive.
Cache buildup also happens because Outlook automatically stores certain data for offline use. This feature allows you to read your emails even when you're not connected to the internet. However, this convenience comes at the cost of taking up storage space. Understanding this basic relationship between cache and performance helps explain why clearing cache periodically can be a useful maintenance task.
Practical Takeaway: Cache is stored data that helps Outlook run faster, but it grows over time and can eventually slow down your computer or take up storage space. Knowing this will help you decide when clearing cache makes sense for your situation.
Clearing Cached Exchange Data in Outlook
One of the most important caches in Outlook is the Exchange cache, which stores copies of your email data from your email server. This cache contains offline copies of your emails, folders, and account information. If you use Outlook with a business email account (typically Microsoft Exchange or Microsoft 365), you have an Exchange cache that you may want to clear periodically.
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The process for clearing this cache differs depending on which version of Outlook you're using. For Outlook on Windows, you'll need to access your account settings. Start by opening Outlook and going to the File menu. From there, select Account Settings and then Account Settings again from the dropdown menu. This will open a window showing all your email accounts configured in Outlook.
In the Account Settings window, find the email account you want to work with and select it. Look for a button that says "Change" or "Repair" depending on your Outlook version. When you click this button, you'll see options related to your account. One of these options will allow you to clear the offline cache or offline data store. The exact wording might be "Clear Offline Data" or "Delete Cached Exchange Data," but the function is the same.
When you clear the Exchange cache, Outlook will delete all locally stored copies of your emails and data for that account. The next time you start Outlook, it will begin re-downloading your email data from the server. This process might take some time depending on how many emails you have. During this period, Outlook may run slowly as it rebuilds the cache. This is normal and temporary.
Practical Takeaway: To clear Exchange cache in Outlook, go to File > Account Settings > Account Settings, select your account, click Change, and look for an option to clear offline data. Be aware that Outlook will need to re-download your data afterward.
Clearing Temporary Files and Outlook Cache Folders
Beyond the Exchange cache, Outlook stores temporary files in specific folders on your computer. These temporary files include cached images, temporary copies of attachments you've opened, and other working files that Outlook creates as you use the program. These folders can accumulate a significant amount of data over time and can be safely cleared to free up storage space.
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The location of these temporary files varies depending on your operating system and Outlook version. On Windows computers running Outlook 2016 or later, the main temporary cache folder is usually located at: C:\Users\[YourUsername]\AppData\Local\Microsoft\Outlook. You'll need to show hidden files to see this folder since AppData is a hidden directory by default. To do this, open File Explorer, click View, and check the box for "Hidden items."
Inside the Outlook folder, look for files with extensions like .ost (Offline Storage Table) or .tmp. The .ost files are your offline cache files. You should not delete these files while Outlook is running, as this can cause problems. Instead, close Outlook completely before deleting any files from this directory. Once Outlook is closed, you can safely delete the temporary files and .ost files. Outlook will recreate these files the next time you open the program.
Another way to clear temporary files is through Windows Disk Cleanup, which is a built-in utility that identifies and removes unnecessary files from your computer. You can access this tool by searching for "Disk Cleanup" in your Windows search bar. When you run Disk Cleanup, it will scan your drives and show you various categories of files you can delete, including temporary files and cache files. Check the boxes for categories like "Temporary files" and "Recycle Bin," then click Delete.
Practical Takeaway: Temporary cache files are stored in hidden folders on your computer. You can manually delete them by closing Outlook, navigating to the AppData folder, and removing .ost and .tmp files, or you can use Windows Disk Cleanup for a simpler approach.
Clearing AutoComplete Cache in Outlook
Outlook maintains an AutoComplete cache that stores email addresses you've typed and sent messages to. This cache helps Outlook suggest email addresses as you type in the To, Cc, or Bcc fields. While this feature is convenient, the AutoComplete cache can sometimes contain outdated or incorrect email addresses, or addresses you no longer want to see in suggestions. Clearing this cache removes all stored email address suggestions.
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To clear the AutoComplete cache in Outlook, start by opening Outlook and going to File menu. Click Options to open the Outlook Options window. In the left sidebar, look for and click "Mail." Scroll down in the Mail settings until you find a section related to sending messages or message composition. You'll see an option that says "AutoComplete List" or "When composing a message, suggest names from the AutoComplete list as you type."
Near this option, there should be a button labeled "Empty AutoComplete List" or similar wording. Click this button, and Outlook will ask for confirmation. Confirm that you want to clear the AutoComplete cache. After clearing it, the list of suggested email addresses will be empty. However, Outlook will start building a new AutoComplete cache immediately as you compose new emails and type recipient addresses.
It's worth noting that clearing your AutoComplete cache is different from clearing your Exchange cache or temporary files. AutoComplete clearing only removes the list of suggested email addresses you've typed before. Your actual emails and email data remain unchanged. Some people choose to clear their AutoComplete cache regularly for privacy reasons or to remove outdated contact information, while others prefer to keep it for the convenience of having address suggestions available.
Practical Takeaway: To clear AutoComplete suggestions in Outlook, go to File > Options > Mail and click "Empty AutoComplete List." This removes stored email address suggestions but doesn't affect your actual emails or data.
Clearing Outlook Web Access Cache
If you use Outlook Web Access (OWA), which is the web-based version of Outlook that you access through a web browser, you may also want to clear the browser cache related to your email account. When you access Outlook through a web browser, your browser stores temporary files, cookies, and cached data from the OWA website. This cache helps the website load faster when you return to it, but it can also accumulate over time and occasionally cause performance issues or display problems.
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Clearing the Outlook Web Access cache is done through your web browser, not through Outlook itself. The process varies depending on which browser you use. If you're using Microsoft Edge, click the menu button (three dots) in the upper right corner and select Settings. Go to Privacy, search, and services. Under Clear browsing data, you can choose what