1. A method comprising: at a computer 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: obtaining a plurality of index entries in an index, a respective index entry corresponding to a respective term in one or more messages, 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; responsive to receiving a first message having a message body and a message header; updating the index by: associating the first message with a conversation having one or more other messages; identifying text in the message body of the first message as quoted text based on text that occurs in one or more of the other messages of the conversation; and adding, to the index, a plurality of first-message index components that each includes an identifier of the first message, including: one or more original text index components that correspond to terms that occur in original text of the message body of the first message; and one or more quoted text index components that correspond to terms in the message body of the first message that occur in the quoted text of the first message; and responding to a search query having one or more query terms by: identifying messages including at least one query term in the one or more query terms by searching the index, wherein the searching distinguishes between (A) matches of a query term with original text index components and (B) matches of a query term with quoted text index components, and preparing a response to the search query that includes search results corresponding to the identified messages; wherein the one or more quoted text index components include information indicating that the corresponding terms are terms in the quoted text of the first message.
1. A method comprising: at a computer 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: obtaining a plurality of index entries in an index, a respective index entry corresponding to a respective term in one or more messages, 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; responsive to receiving a first message having a message body and a message header; updating the index by: associating the first message with a conversation having one or more other messages; identifying text in the message body of the first message as quoted text based on text that occurs in one or more of the other messages of the conversation; and adding, to the index, a plurality of first-message index components that each includes an identifier of the first message, including: one or more original text index components that correspond to terms that occur in original text of the message body of the first message; and one or more quoted text index components that correspond to terms in the message body of the first message that occur in the quoted text of the first message; and responding to a search query having one or more query terms by: identifying messages including at least one query term in the one or more query terms by searching the index, wherein the searching distinguishes between (A) matches of a query term with original text index components and (B) matches of a query term with quoted text index components, and preparing a response to the search query that includes search results corresponding to the identified messages; wherein the one or more quoted text index components include information indicating that the corresponding terms are terms in the quoted text of the first message. 5. The method of claim 1 , further comprising: after identifying quoted text in the first message: receiving a second message that is a prior message in the conversation; associating the second message with the conversation; and updating the quoted text in the first message based on the text that occurs in the second message.