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 Office365 account:
1) In the top menu bar of your Office365 Outlook account, go to "Manage integrations"
2) Type 'yoxel' in the search box and you should see the add-in. Activate it.