1. A computer-implemented system for identifying near duplicate messages, comprising: a message grouping module to group by conversation thread, messages each comprising a content body, wherein one or more of the messages also includes an attachment; a message sorting module to sort the messages for each conversation thread in order of message length; a message selection module to select for one of the threads at least one of the messages and to compare the body of the selected message with the body of one such shorter message in that thread; a determination module to determine that the body of the shorter message is included in the body of the selected message; a message comparison module to compare hash codes of the attachments for the selected message and the shorter message; and a message marker to mark the shorter message as a near duplicate message of the selected message when the hash codes of the attachments match.