15. A computer-implemented method of processing messages, comprising: at a server computer system having one or more processors and memory storing one or more programs, the one or more processors executing the one or more programs to perform the operations of: receiving a plurality of messages directed to a user, each message having a unique message identifier; associating each of the plurality of messages with a respective conversation, each conversation having a respective conversation identifier; wherein each conversation comprises a set of one or more messages sharing a common set of characteristics that meet first predefined criteria and the respective conversation identifier is distinct from a subject reference of the one or more messages in the respective conversation; associating with each conversation a set of senders of messages included in the conversation; and providing presentation information for displaying a list of conversations in an order determined in accordance with second predefined criteria, each conversation being represented as a single item in the list, wherein a plurality of conversations in the list of conversations each include a plurality of messages that share a common set of characteristics that meet the first predefined criteria; wherein providing presentation information includes providing information to display the list of conversations as a set of rows, each row corresponding to one of the listed conversations and including at least a sender list, a conversation topic and a date/time value, wherein the sender list of a row in the list of conversations includes identifiers of one or more senders of at least one message in the corresponding conversation, including identifiers of a plurality of the senders in the set of senders, but less than all of the senders in the set of senders, when the set of senders exceeds a predefined limit.
15. A computer-implemented method of processing messages, comprising: at a server computer system having one or more processors and memory storing one or more programs, the one or more processors executing the one or more programs to perform the operations of: receiving a plurality of messages directed to a user, each message having a unique message identifier; associating each of the plurality of messages with a respective conversation, each conversation having a respective conversation identifier; wherein each conversation comprises a set of one or more messages sharing a common set of characteristics that meet first predefined criteria and the respective conversation identifier is distinct from a subject reference of the one or more messages in the respective conversation; associating with each conversation a set of senders of messages included in the conversation; and providing presentation information for displaying a list of conversations in an order determined in accordance with second predefined criteria, each conversation being represented as a single item in the list, wherein a plurality of conversations in the list of conversations each include a plurality of messages that share a common set of characteristics that meet the first predefined criteria; wherein providing presentation information includes providing information to display the list of conversations as a set of rows, each row corresponding to one of the listed conversations and including at least a sender list, a conversation topic and a date/time value, wherein the sender list of a row in the list of conversations includes identifiers of one or more senders of at least one message in the corresponding conversation, including identifiers of a plurality of the senders in the set of senders, but less than all of the senders in the set of senders, when the set of senders exceeds a predefined limit. 19. The method of claim 15 , wherein the date/time value in a row of the set of rows comprises a date/time value associated with a most recent message of the conversation that satisfies a query.