Ned Culhane '06 pointed to the recent publication of "Send: The Essential Guide to Email for Office and Home." A good interview with the authors here, with some discussion of the do's and don'ts.
One thing I don't see often mentioned is that students need to junk or sequester those email addresses they created before college if they crafted monikers that no longer look so cool. I personally feel funny answering emails from students who have addresses like "maxipimp" or "Soawesome". Or if you can't part with that hip part of your existence, don't use it for formal email, having your UPS email routed there (instead of vice versa).
And don't forget to send return emails to acknowledge the end of a communication if you've initiated it. Employers and others appreciate a final email, especially if it provides some sense of resolution and an expression of appreciation for their efforts on your behalf. If you're asking someone to do something for you, it's your job to wind up the conversation and thank them for their time.
