I’ve never given much thought to improving my email system until I watched a video of a lecture on time management given by Randy Pausch where he lambasted email systems. Everyone is concerned about filtering spam, but amazingly it seems like little has been done to filter and categorize all incoming email.
Microsoft has an interesting research project named Snarf (I like that name) that addresses some of the email triage issues.
SNARF was built around the notion that social network information that is already available to the computer system can be usefully reflected to the user: a message from a manager might be seen differently than a message from a stranger, for example. SNARF applies this idea to email triage: handling the flow of messages when time is short and mail is long.
Other good email triage information can be found here.