How to clear the Outlook cache?

As an integral part of the Microsoft Office package, Outlook is one of the most popular e-mail programs. The mail client permanently uses a cache for everyday routines. However, this so-called Outlook cache can cause problems and noticeably slow down the software. In such cases you should clean Outlook and clear the Outlook cache. Strictly speaking, you are not dealing with just one, but with several temporary and intermediate caches. Here, we explain how to clear Outlook’s e-mail cache and auto-complete list in addition to the attachment cache.

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Why should you delete the Outlook cache?

The Outlook cache is an operational working memory that is hidden in the background to speed up working with the mail program and enable faster file access. For example, the software deposits e-mail attachments in the cache, which are temporarily stored there for viewing.

Tip

In addition to mail programs, browsers also use a cache. Empty your cache regularly to guarantee fast surfing.

Roughly speaking, the cache memory can be compared to the storage area of a desk, where the most important working material is stored for quick access. If the materials are no longer needed, they are put away to free up space again. However, if you don’t tidy up your desk regularly, you will eventually suffer from a lack of space and lose track of everything. Convenient and quick access to permanently required working materials then no longer works.

It’s a similar process on the computer. Normally, the Outlook cache is cleared regularly, so that temporarily storedfiles do not remain on the hard disk permanently and disappear through automated deletion procedures. However, this does not always work. For example, if you have opened an attachment (such as images, documents, or pdf files) and close Outlook first, the data may permanently be stuck in the cache.

Fact

A cache is not intended for long-term storage. If you want to back-up your e-mails, you should archive Outlook data.

Over time, an untidy cache will accumulate these kinds of dead ends. The larger the volume of cache data, the longer it takes to read the cache. Corrupted files can also have a negative effect on the performance of the e-mail program. When you notice that Outlook is no longer acting as smoothly as it should, the Outlook cache should be cleared. Since e-mails often contain confidential information, you can also optimise data protection by deleting the temporary files and preventing unwanted access to private information. In addition, you’ll free up valuable storage space. Since cache files are not essential for the functioning of the program, nothing happens during the clean-up process. In our tutorial, we’ll show step-by-step instructions how to delete the different Outlook caches.

How can the Outlook cache be emptied?

First things first: if Outlook is open, you will need to close the program. Otherwise, deleting an Outlook cache will not work. The rest of the procedure is not particularly complicated, you only need a few steps to clean Outlook.

Delete attachments cache

Step 1: Search for the cache folder

To clear the attachment cache, first activate the search box in the Windows taskbar at the bottom left of the screen (if it is not displayed, click the magnifying glass at the left edge of the taskbar). Now you need to enter the following path into the search box (step 1 in the screenshot below):

 

%userprofile%\AppData\Local\Microsoft\Windows\INetCache\Content.Outlook

Step 2: Open the cache folder

Next, click on “Open” (step 2 in the screenshot) or press the ENTER key on the keyboard:

Note

The user profile variable (%userprofile%) is a convenient way to abbreviate path entries. Windows independently replaces %userprofile% with the current user’s account data, such as “C:\Users\Peter\”. The full path to the cache for Peter’s user profile: C:\Users\Peter\AppData\Local\Microsoft\Windows\INetCache\Content.Outlook.

Step 3: Delete the Outlook cache folder

Shortly after this, Explorer will open with the Outlook folder of your user profile. Here, you will find the cache folder. Outlook generates this folder automatically and gives it an individual name, that differs on each computer. In our example a folder with the name “2E3R8BQM” was created. The folder can now be deleted directly. If there are several directories, you can also remove several folders to clean up Outlook thoroughly:

You can also selectively delete specific contents when clearing your Outlook cache by clicking the cache folder and selecting files with the mouse:

Summary: clearing the Outlook cache

  1. Close Outlook
  2. Call up %userprofile%\AppData\Local\Microsoft\Windows\INetCache\Content.Outlook via the search bar
  3. Remove selected files and folders
  4. Launch Outlook

Delete the e-mail cache

If necessary, there is a second Outlook cache that can be cleared, which is responsible for the offline operation of Outlook and ensures smooth working even when connections are slow or temporarily disrupted. The local cache that is used for IMAP accounts, Microsoft 365 accounts, Exchange accounts, and Outlook.com accounts, is kept up-to-date by Microsoft through regular synchronization operations between the mail client and the server (the update happens in the background while you are online). The local cache is stored for each Outlook profile in the form of an OST file (offline-storage-table-file).

Tip

In combination with Microsoft Exchange you can extend Outlook to a professional groupware solution. The collaborative software environment makes it easy to share work processes and integrate many additional cloud-based functions into your digital processes.

In some circumstances, this particular cache file causes problems. It is more prone to corruption the larger it becomes, affecting whether Outlook functions properly. For example, if Outlook doesn’t start up, an oversized OST file could be to blame. If several people use a shared e-mail account and make changes (e.g., moving a bunch of e-mails while cleaning up), this can also cause problems. Outlook will delete and then automatically rebuild an OST file to ensure that folders or e-mails that have disappeared are displayed correctly again, for example.

Tip

Normally it’s no problem to delete an OST file, because it’s a client-side copy of server data that is automatically rebuilt by Outlook. However, you can make a backup of the file before Outlook cleans it up, just to be on the safe side, or simply move the OST file to a backup directory. (When moving the file there is no need to delete the cache file). In that case, you’ll need some patience and sufficient disk space, because the files can become very large – several GBs are not uncommon.

These steps are essential to delete your e-mail cache in the Windows AppData folder:

Step 1: Search for the e-mail cache folder

First, enter the following path in the Windows Explorer address bar or in the Windows search bar:

 

%userprofile%\AppData\Local\Microsoft\Outlook 

Step 2: Delete the OST file

The folder with the OST file will open and you can delete it. Make sure that Outlook is closed during the clean-up process. If you manage several Outlook profiles from a single PC, you will find several files with the extension *.ost. The OST file extension is preceded by the name of the Outlook profile (e.g., peter@google-mail.com.ost):

Step 3: Restart Outlook

After clearing the Outlook cache, you can restart the mail client. Depending on the size of the mail archive, it may take some time until the OST file is regenerated, and the original state of the profile is restored.

Note

If you do not see the AppData folder, you need to first make it visible in Windows Explorer. In our tutorial, we’ll show you how to make the Windows AppData folder visible.

Quick guide: how to empty your e-mail cache

  1. Open %userprofile%\AppData\Local\Microsoft\Outlook
  2. Close Outlook
  3. Delete OST files
  4. Restart Outlook

How to clear the Outlook Auto-Complete List?

The Auto-Complete List is useful in everyday life. This collection of addresses saves Outlook users a lot of paperwork and speeds up sending e-mails. However, if it becomes too extensive over time, its usefulness diminishes. The list also stores outdated or even incorrect addresses that are the result of typing errors. If there are too many entries, it can happen that the wrong addressees are selected by mistake. This is the case, for example, when similar names are hastily added to an address list of a circulating e-mail.

Tip

Use Outlook even more efficiently in the cloud-based work environment that is Microsoft 365. The Office suite gathers many useful Microsoft products that can optimise your daily workflow.

Individual suggestions can be manually removed from the complete list. If you point to an entry with the mouse, an “X” appears to the right of the name entry. If you click on it, the person’s name and e-mail address will be deleted from the AutoComplete List. If you want the list to be completely cleared and rebuilt when Outlook is cleaned up, you need to do the following:

  1. Start Outlook and select the menu item “File”.
  2. Open the Outlook settings via the “Options” entry at the bottom left of the screen:
  1. In the options menu that opens, select the entry “Mail” (see point 1 in the below screenshot).
  2. The auto-complete setting is listed under the “Send messages” section (item 2 in the screenshot). (If it is not visible at first, please scroll.)
  3. Then use the corresponding button to clear the “Auto-Complete List” (item 3 in the screenshot):
  1. Finally, confirm the deletion of the Auto-Complete List by clicking on the “Yes” button.

With this final step, you have cleared another Outlook cache.


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