John Porcaro talks about wading through all that email :

Use subject-line protocols to speed communication: a.) No reply needed – NRN; b.) Thank you - TY; c.) Need response by date and time – NRB 10/30 3:00 pm; d.) Use subject line for whole message: Meet 10:00 10/30 Okay?

Determine who needs to be copied on what, what needs to be read, and what needs to be filed.

Keep e-mails short. Most should be no more than 1-10 sentences. Communicate your main point in the first sentence or two. Don't make readers work because you don't have time to focus.

...via Cutting Through