How to Clear the Outlook Cache

Delete Microsoft Outlook's Cached Data

MS Outlook 2016 logo


Microsoft Outlook stores files you've already used so that it can easily get them again should you request them. These files are known as cached files, and they can be safely deleted should you need to.

You might want to clear out the Outlook cache if old data still remains even after you tried deleting it, something that often happens when removing and reinstalling Outlook add-ins.

Another reason to delete Outlook's cached files is if autocomplete data or other "behind-the-scenes" information is still popping up even after you've deleted contacts or reinstalled the whole program.

Removing the cache in Outlook does not delete emails, contacts, or any other useful information. The cache is only there to help speed things up in some circumstances, so there's no need to think that it will delete any of your personal information.

Open the Microsoft Outlook Data Folder

Run program


For starters, make sure MS Outlook is completely closed down. Save any work and then exit the program before continuing.

  1. Open the Run dialog box with the Windows Key + R shortcut.
  2. Copy and paste the following into the dialog box:
    Type %appdata%\Microsoft\Outlook if you're using Windows 2000 or XP.
  3. Press Enter.

A folder will open to Outlook's data folder, which is where cached files are stored.

Select the "extend.dat" File

Screenshot showing the "extend.dat" file selected in the Outlook folder


There should be multiple files and folders listed here, but there's only one that you're after.

All you need to do now is select the DAT file that Outlook stores the cache in. This file is called extend.dat like you see in this screenshot.


Delete the DAT File

Delete the DAT File


Delete the extend.dat file by pressing the Delete key on your keyboard.

Another way to remove this DAT file is to right-click it or tap-and-hold, and then select Delete from the context menu.

In some situations, it's smart to back up the file you're about to delete so that you can restore it should something go wrong. However, Outlook will automatically make a new extend.dat file after you delete it and open Outlook again. We're removing it to clear the cache contents and allow Outlook to use it again with a fresh start.

Now that the old extend.dat file is gone, you can now reopen Outlook so that it will start using a new one.