E-mail is absolutely an awful way to communicate with people. Orion, who works with me at Terracotta, and I joke about this all the time. More lost information, mistakes, fights and miscommunication can be attributed to e-mail than almost any other cause I can think of. Here are a few of the problems with email communication that I’ve noticed over the years:
1. It is almost impossible to properly convey emotion in e-mail (so don't try).
2. Most people only skim e-mails because they get so damn many of them
3. E-mail is slow and problematic for conversations
4. E-mail is permanent.
Here are some rules that I try (and fail sometimes) to follow.
1. Never try to express anything but the simplest of emotions via e-mail. You can't see the persons face, or even make judgments based on communication pauses or tone. So don't send emotion in e-mail.
2. Don't send e-mail if you are angry. (Alex miller pointed out that it is often helpful to write the angry e-mail but not send it. It's a good way to vent). Always make your e-mail twice as positive and/or emotionless as you think you need to. As they say on dragnet: Just the facts ma’am.
3. Don't assume that your e-mail was read. How many times have you heard, "But I sent an e-mail." Doesn't mean squat. Check in with people on chat, drop by, or call and make sure that they got/understood your e-mail. If you didn't get an ack (geek for response), you should assume that they didn't get it. Let me say it again. Don't ever defend yourself with "I sent an e-mail"
4. If you want to have a conversation, use a synchronous communication mechanism like chat, irc, talk in person or on the phone. E-mail is strictly good for relaying facts (and not even very good for that because they get lost in the ton of other e-mails you have. Try a wiki for facts).
5. If you send a dumb e-mail be assured that the receiving person has passed it around to a few friends to get a laugh or opinion. It is a permanent record of your stupidity (kind of like this blog is for me). So don't say anything in e-mail that you don't want to see on the cover of the NY times.
I must admit that I learned some of the above the hard way. I assume most people have received an e-mail that made their blood boil. You’re just dying to write up a response outlining what a jerk someone is. Well don't do it!
The thing to keep in mind is that there are a million ways to get yourself into trouble with email, but you almost never get yourself into trouble by NOT sending one.