From the Alban Institute:

1. E-mail makes it impossible to read the non-verbal body language of the persons with whom you are communicating.  Likewise, they can’t read yours. I have occasionally made the mistake (perhaps you have, too) of trying to crack a joke through e-mail and having it fall flat. I can’t read the body language to tell how the joke is being received, and others can’t see the twinkle in my eyes when I am joking.  When a congregation is in conflict, folks are already very emotionally reactive.  Therefore, people in this situation are far more likely to misread or misinterpret what is being said under the best of conditions.  Eliminating visual cues and vocal inflection further cripples the communication process and opens the door to misinterpretation and misunderstanding.
2. E-mail appears to be fast, almost immediate, communication, when in fact the length of time it takes to deliver a message depends largely on the recipient’s personal habits.  Some people check their Blackberrys or iPhones for messages every few minutes, and some go for days without turning on their computer to look at their e-mail.  The uncertainty around when a message is received often adds to the confusion of who knows what and when they heard it—often a central communication issue in conflicted situations.
3. Because e-mail language is often less formal than traditional written language, it feels much more like talking on the telephone, except that it is a one-sided conversation.  Your e-mail message probably makes perfect sense to you.  But it may contain unspoken assumptions, or even a typo that can change the meaning of the message for your recipient, and complicate your effort to communicate.  It can actually take longer to sort out miscommunication than it would to relay information in face-to-face conversations, one at a time.  I frequently have to tell pastors to stop using e-mail when trying to deal with a parishioner’s difficult behavior, and simply go talk to them.   A face-to-face conversation, with give and take, can often serve to sort out a complicated situation when a one-sided e-mail message only makes it more complex.
4. E-mail is not confidential. No matter what kind of disclaimer or warning about confidentiality you include in your e-mail, anyone can forward any e-mail at any time. When I am about to send out an e-mail message, I always ask myself, “Would I feel comfortable if this e-mail were forwarded to someone else—even if it was accidentally forwarded?”  If your answer to that question is “no,” then don’t send it.  And that is related to another practice you might want to develop: get in the habit of re-reading any e-mail message before sending it out.  Usually, you will just catch typos and the occasional omitted word, but sometimes, you will hear a very different message than the one you intended.  Train yourself to pause and re-read before you hit the send button.
5. E-mail is not a constructive venue for important conversations.  One of the strengths of e-mail is its ability to communicate details quickly and efficiently.  Important conversations, and especially those that surround a conflicted situation, need and deserve richer and fuller interaction—one in which nuance and non-verbal communication is part of the communication process.