E-mail is fast and effective, but it's also potentially risky: Without body language or tone of voice to guide them, recipients may wind up taking offense to what you write. It is especially true in back-and-forth chains that can devolve into frustrated knee-jerk responses, writes Peter Post on the Boston.com site. "Any time you begin to sense that the thread is becoming unpleasant, that is the moment to pick up the phone or visit the person to resolve the issue," he advises.