In this study, an email-based community supporting a community of practice (CoP) of mathematic teachers was investigated. Public messages members send were examined in order to determine what activities that were conducted by the members and what their level of participation is. Data was gathered via a “Media Records Evaluation Form”. A content analysis of these messages revealed that the most frequent activity was views/chat, followed by appreciation and knowledge sharing. Findings also indicate that the least activities were apology, administrative and congratulations. In a CoP, membership is a personal matter and members represent different aspects of participation. In this sense, members’ level of participation were determined by using clustering analysis. The results show that there are five different types of participation defined as community leader, core members, active members, peripheral members and active lurkers. However, research findings also point at a sixth group who never participate in knowledge sharing and exchange.