KB10392143

Open Outlook and click on Tools Options

Now click on the Other tab and click the AutoArchive button.

This opens up a whole menu of options and settings to pick from:

you can choose how often AutoArchive runs in X days. Also confirm how old the archived emails should be under During AutoArchive

Once its all configured Make sure to click the Apply these settings to all folders now button

Once you are done go to File then Archive

Click the Mailbox and then Ok

after you hit Ok the above window will go away

Look down into the bottom corner of Outlook and you will see this Archiving animation 

Once the Archiving animation disappears you are done