To access Cached Exchange Mode Settings:

1. Open up your Outlook app.
2. Click on "File" menu in the top left then click "Account Settings" then "Account Settings" again.
3. Select your email account then click "Change...".
4. Ensure "Use Cached Exchange Mode" is checked then click "Next".
5. Use the slider to select what mail you want to keep cached on your computer.
6. Click "Finish".

This will make Outlook store a local copy of your email on your computer. Keeping a local cache on the computer will improve your experience by providing quicker access to your most-accessed emails.