Email-Based Promotion for User Adoption

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium to increase product usage. In some examples, a request to assign a task to a selected user is received. The selected user as a non-user of the task service. In response, task information and an identification of the task service is appended to an electronic document. Once the selected user has subscribed to the task service, the selected user is assigned to the task within the task service.