A web add-in is a web-based add-in. Such a web-based add-in does not need to be installed locally on each machine on which it is to be used. Rather, a Web Add-In is cloud-based and must be deployed by the Microsoft 365 Exchange administrator or by the global administrator account of the respective company, association, agency or institution. A web add-in can be used for web applications as well as desktop applications. For example, there are signature web add-ins, i.e. web add-ins for e-mail signatures in Outlook - Outlook on the Web (OWA, Web App) or Outlook for Windows. Modern web add-ins replace the classic COM add-ins (COM = Component Object Model). You have to decide whether you want to use a web add-in or a COM add-in. It is not possible to use both types of add-ins at the same time. Besides COM add-ins, there are other types of add-ins, such as the so-called automation add-ins, for example for MS Excel.