For an Outlook add-in, Outlook reads the manifest and hooks up the specified controls in the UI, and then loads the JavaScript and HTML. Unlike COM add-ins, Outlook add-ins don't have any code physically installed on the user's device or Outlook client. Outlook add-ins are different from COM or VSTO add-ins, which are older integrations specific to Outlook running on Windows. Outlook add-ins can be acquired from AppSource or sideloaded by end-users or administrators.Outlook add-ins consist of a manifest, which describes how the add-in integrates into Outlook (for example, a button or a task pane), and JavaScript/HTML code, which makes up the UI and business logic of the add-in.The same add-in and business logic works across desktop (Outlook on Windows and Mac), web (Microsoft 365 and ), and mobile.Outlook add-ins are integrations built by third parties into Outlook by using our web-based platform.
