Some 2.7 trillion e-mails will have been sent by people around the world by the end of this year alone. If you feel the majority of them are ending up in your in-box, you're not the only one. E-mail fatigue has become a common business complaint. Increasingly, co-workers seem to figure there's no point in walking 10 feet to a colleague's desk and having a brief conversation when a 300-word e-mail mini-essay will do.