As teachers, you probabaly use email often to respond to questions and concerns from your students. An interesting article titled, “It's All About Me: Why E-Mails Are So Easily Misunderstood” discusses some of the problems with using this form of communication.
Email does not give us cues such as tone of voice, facial expressions, and body language.
The ability to instantly reply to email leads people to think and write quickly without thinking through what they're saying and how it might be perceived (hence, the large number of spelling and grammatical errors by our students).
Email does not convey emotion or a personal rapport and thus can convey a message different from what you intended.
"According to one study, e-mail users have only a 50-50 chance of correctly interpreting the intended tone of an e-mail."
How to avoid problems with email? "Read it aloud in the opposite way you intend, whether serious or sarcastic. If it makes sense either way, revise." And if you are discussing sensitive issues or having a conflict with your student, communicate in person or by phone.