1. A method comprising: at a server having one or more processors and memory storing one or more programs for execution by the one or more processors so as to perform the method: storing a plurality of index entries in an index, a respective index entry corresponding to a respective term and having a plurality of index components, a respective index component of the respective index entry identifying a message that is associated with the respective term; receiving a first message; associating the first message with a conversation having at least one other message; and storing, in the index, a plurality of first-message index components that each include an identifier of the first message, including: one or more index components indicative of a plurality of message terms in the first message; and one or more index components indicative of one or more conversation terms in the conversation, the one or more conversation terms comprising one or more terms that are not in the first message; wherein a respective first-message index component indicative of a conversation term in the conversation includes a value identifying the respective index component as being associated with a conversation term not in the first message.
1. A method comprising: at a server having one or more processors and memory storing one or more programs for execution by the one or more processors so as to perform the method: storing a plurality of index entries in an index, a respective index entry corresponding to a respective term and having a plurality of index components, a respective index component of the respective index entry identifying a message that is associated with the respective term; receiving a first message; associating the first message with a conversation having at least one other message; and storing, in the index, a plurality of first-message index components that each include an identifier of the first message, including: one or more index components indicative of a plurality of message terms in the first message; and one or more index components indicative of one or more conversation terms in the conversation, the one or more conversation terms comprising one or more terms that are not in the first message; wherein a respective first-message index component indicative of a conversation term in the conversation includes a value identifying the respective index component as being associated with a conversation term not in the first message. 10. The method of claim 1 , further comprising: storing, in the index, a first-message index component that identifies the first message as a representative message of the conversation.