1Download the add-in here from the Microsoft AppSource marketplace. You can also add it directly in the "Apps" icon in Outlook, and click the option "Add apps", and search for InFiler.
2Once installed, you can open any email and launch InFiler from the Apps icon to start using it.
And you're all set! InFiler does not require you to create a separate account, you're automatically logged in through Microsoft SSO.