Abstract: Methods and apparatuses for identifying groups of electronic messages, generating conversation documents using the groups of electronic messages, and indexing the conversation documents to improve search ranking and retrieval for content contained within the electronic messages are described. In some cases, understanding the contents of a group of electronic messages may require context from outside the group of electronic messages, such as context provided by electronic messages outside of the group of electronic messages or context provided by electronic documents linked to by messages of the group of electronic messages. The identification of a group of electronic messages includes detecting a conversation boundary that separates a first set of messages from a second set of messages, which may be determined using machine learning approaches or various heuristics.