Ten Steps for Cleaning Up Information Pollution (Jakob Nielsen's Alertbox): "Don't check your email all the time. Set aside special breaks between bigger projects to handle email. Don't let email interrupt your projects, and don't let the computer dictate your priorities. Turn off your email program's 'Biff' feature (the annoying bell or screen flash that notifies you every time an email message arrives). If you're using Microsoft Outlook, go to Tools > Options > Preferences > E-mail Options and uncheck 'Display a notification message when new mail arrives.'
Don't use 'reply to all' when responding to email. Abide by the good old 'need to know' principle that's so beloved by the military and send follow-up messages only to those people who will actually benefit from the reply.
Write informative subject lines for your email messages. Assume that the recipient is too busy to open messages with lame titles like 'hi.'
Create a special email address for personal messages and newsletters. Only check this account once per day. (If you're geekly enough to master filtering, use filters to sort and prioritize your email. Unfortunately, this is currently too difficult for average users.)
Write short. J. K. Rowling is not a good role model for email writers.
Avoid IM (instant messaging) unless real-time interaction will truly add value to the communication. A one-minute interruption of your colleagues will cost them ten minutes of productivity as they reestablish their mental context and get back into 'flow.' Only the most important messages are worth 1,000 percent in overhead costs"