1. A method comprising: at a computing device having one or more processors and memory storing one or more programs for execution by the one or more processors: responsive to a determination that a message body of a first electronic message satisfies a first set of content-based clustering rules associated with a first message cluster: assigning the first electronic message to the first message cluster, and displaying a first cluster graphic for the first message cluster, wherein the first cluster graphic is characterized by (a) a first state in which messages in the first message cluster are individually depicted and (b) a second state, which replaces the first state upon user input and that collectively represents a plurality of messages in the first message cluster, wherein each message in the first message cluster is either (i) addressed at least to a first recipient or (ii) originates from the first recipient.