1. A method for conversation detection in email systems, comprising: providing a computer system, wherein the system comprises distinct program modules embodied on a computer-readable medium, and wherein the distinct program modules comprise a conversation detector; executing the conversation detector to group email messages into first groups, each of the first groups having a common core subject to thereby define a conversation by applying a similarity function a first time based on a similarity of the email messages' attributes, the similarity function including: a similarity between the email messages' participants; at least one of a similarity between the email messages' subjects and a similarity between the email messages' contents; applying the similarity function a second time to group the email messages of the first groups into respective second groups; and defining the second groups as sub-conversations.