1. A method of managing messages, comprising: on a server system having one or more processors and memory: storing a plurality of conversations, each of the conversations having a respective conversation identifier and comprising one or more messages sharing a common set of characteristics that meet predefined criteria; storing a plurality of labels, including a first label associated with messages from multiple conversations of the plurality of conversations; sending, to a remotely located client system, first display information enabling the client system to display a user interface including a first label affordance for the first label, wherein the first label affordance is configured to, in response to selection of the first label affordance, cause a first predefined request for conversations having messages associated with the first label to be transmitted from the client system to the server system; after sending the first display information to the client system, receiving the first predefined request from the client system; and in response to the first predefined request: producing a first list of conversations in accordance with a criterion that all conversations in the first list of conversations include at least one message associated with the first label, wherein a plurality of the conversations in the first list each include a plurality of messages, and producing the first list of conversations includes accessing an index of the conversations that includes an index entry for the first label, wherein the index enables the messaging system to identify messages associated with a respective label in response to a search query that includes a search term corresponding to the respective label; and sending, to the client system, second display information enabling the client system to display the first list of conversations.