18. The computer readable storage medium of claim 15 , wherein the first display information includes information enabling the client system to display as part of the user interface, a plurality of respective label affordances for respective labels, wherein each respective label affordance is configured to, in response to selection of the respective label affordance, cause a respective predefined request for conversations having messages associated with the respective label to be transmitted from the client system to the server system.
18. The computer readable storage medium of claim 15 , wherein the first display information includes information enabling the client system to display as part of the user interface, a plurality of respective label affordances for respective labels, wherein each respective label affordance is configured to, in response to selection of the respective label affordance, cause a respective predefined request for conversations having messages associated with the respective label to be transmitted from the client system to the server system. 20. The computer readable storage medium of claim 18 , wherein the plurality of respective label affordances includes a second label affordance associated with a second predefined request for messages associated with a second label, and the one or more computer programs further comprises instructions which, when executed by the server system, cause the server system to: after sending the first display information to the client system, receiving the second predefined request from the client system; and in response to the second predefined request: produce a second list of conversations in accordance with a criterion that all conversations in the second list of conversations include at least one message associated with the second label, wherein a plurality of the conversations in the second list each include a plurality of messages; and send, to the client system, third display information enabling the client system to display the second list of conversations.