9. A conversation-based message system, comprising: a server with one or more processors and memory, the memory storing one or more programs configured for execution by the one or more processors, the programs including: a conversation matching module that matches at least one of a plurality of received messages to a conversation in a plurality of conversations, each of the plurality of conversations having one or more messages sharing a common set of characteristics that meet predefined criteria; a message database that stores messages and associated information, including conversation information; a conversation search module that returns a list of conversations in response to a search query, wherein at least one of the conversations in the list includes a plurality of email messages; a formatting module that associates formatting information with at least one of the conversations in the list of conversations, wherein the formatting information includes differentiating information that differentiates one or more first messages in the conversation relevant to the search query from one or more second messages in the conversation not relevant to the search query, wherein the differentiating information includes formatting information for the first messages in a first format and formatting information for the second messages in a second format, and the first format differs from the second format in a visually distinctive manner; and a send module that transmits the list of conversations and the formatting information.
10. The system of claim 9 , wherein the first formatting information is associated with an expanded mode of display and the second information is associated with a compacted mode of display.