You can Install Yoxel Inbox app from the Office365 store using the following link: Yoxel Mailbox Assistant

You can also install the add-in while you're in your Outlook:

1) Click the "Store" button in the Outlook ribbon:

2) Type 'yoxel' in the search box and you should see the add-in. Click 'Add' to install it.

3) Once the add-in is installed select an email to read in your Inbox and you should see the Yoxel add-in button in the Outlook ribbon.  Click the buttonto open the task pane (side bar) and follow the Authorization prompts to activate the add-in., users may have to use the username/password based mode to active the add-in.