The rapid growth of mobile devices and mobile communication technologies in recent years has created a huge potential for enabling collaborative work. Usually, a collaborative work is usually composed of multiple tasks and participants. Therefore, messages or information sharing among the group is an issue. In order to avoid SPAM and missing messages, there should be a system to check the messages and recognize all relevant receivers. In this paper, a modeling notation is proposed to model and evaluate the relationship among tasks, users, and messages. A project-based task analysis and an authority-recognition model are used to identify receivers regarding their correspondent tasks. Therefore, members in the system can easily share information without being bothered by SPAM or worrying about missing any important messages.