The software company WordRake has a wonderful blog post series about e-mail communication, and one piece of information is particularly startling:
What's an e-mailer to do? Your best bet is to think before you hit the send button. Save a draft of your e-mail and revisit it in an hour or two. This approach might increase your odds of responding thoughtfully to an e-mail rather than merely reacting.“People consistently overestimate their ability to communicate effectively with email.” A 2010 study found that “participants lied 50% more when they negotiated over email compared with pen-and-paper.” One of the reasons, surmised researchers: “Emails are less permanent: it feels closer to chatting than writing a letter.”
You might also consider creating a rule in Outlook to time-delay all your sent e-mails by three-to-five minutes. You can hit send, then change your mind a few minutes later to re-read, double-check who you've sent the e-mail too, and possibly delete the whole thing if you've since come to your senses. This approach can save you from the countless lawyer e-mail blunders that make headlines.
Remember: e-mail is permanent. You can't really retract it once it's been sent, so think twice or four or five times before hitting "send."