From Tim Sanders, author of The Likeability Factor.
1. Never say "no" or disagree over email. Pick up the phone.
2. Don't send an email at a time when you wouldn't normally call the person. If that's the only time you have to write your email, switch to Work Offline.
3. Leave the safety on (or delete the name in the To: line). This will save you from sending something you really don't want to or aren't ready to.