Immersion is a web-based tool developed at MIT Media Lab. It enables the analysis and visualization of mail flow data as networks. (Flow data is understood here to mean the From, To, Cc and Timestamp fields of the emails in the account you are signing in with.) Use of the tool requires that you authorize Immersion to access your email account flow data via OAuth, essentially providing a trust between your email and immersion for the time you use the tool. Results are displayed as a network, in an interactive, dynamic and rich visual display. All aspects of the flow data are leveraged in some way, allowing you to explore the relatedness of senders and receivers, and relative volumes, over time. Your results can be deleted on exit, or saved in Immersion. For more information about Immersion, especially with respect to what specifically it has access, please read the FAQs section of the site.
If you are shy to try this out with your own account, there is a demo available.