Known for its internal plurality, the 'movement for alternative globalization' regularly comes together in events such as the European Social Forum (ESF), which are integral to the process of networking and cross-fertilization among its diverse participants. Yet apart from physical meetings, 'alter-globalization' activists also meet in a variety of online spaces. This article investigates the role of such spaces in the communicative process of collective identity construction by examining three email lists devoted to the organizing of the London 2004 ESF - a European list, a national and a national-factional. Considering collective identity formation as a communicative process, the article has focused on the design of the selected lists and the social context or 'we' that each one helped constitute. It also explored the communicative affordances of the lists for the process of collective identity formation by looking at bonding, trust-building and interactivity. The results show that depending on their purpose, accessibility and geographical scale, the email lists served as distinct but overlapping loci of collective identity. These settings displayed varying degrees of breadth and heterogeneity in terms of their themes and focus, their types of author, as well as the language in which messages were written. They also exhibited different degrees of interactivity with the factional list helping the formation of a cohesive collective identity for its members, while the European one allowed the emergence of a much looser, open and fragmented sense of the collective.