Frequently Asked Question
You can go to Outlook > File tab > Account Settings > Account Settings > click an account > Change button to find the slider that lets you adjust the setting tfrom 12 months to All.
Note that you'll have to restart Outlook before the new setting will take full effect and it may take quite a while for Outlook to download all your messages.
Screen 1: File tab > Account Settings > Account Settings
Screen 2: Click on an account then click the Change button.
Screen 3: Move the slider from "12 months" to "All", then click Next.
Complete the process by clicking Finish button and you will be directed to restart Outlook.