according to Thomas
1. I keep my messages brief and to the point. Sometimes what I need to say is more than three or four brief paragraphs. That’s when I write a letter or ask for an appointment.
2. I don't discuss multiple subjects in a single message. This helps with keeping them brief. If multiple subjects need to be addressed, multiple messages with clear subject lines make life easier for the recipients. It also makes it more likely that I get a response to each of my questions or requests.
3. I never put in an e-mail message anything that I wouldn't put on a postcard. Email can be forwarded, and I have no control over that. I do have control over the content of what I write in my email, though.
4. I send group e-mail only when it's useful to every recipient. I use TO: for the people I expect a response from. I use CC: for people who need to know, but from whom I don’t expect a response. I use BCC: for large groups (primarily to keep all the unnecessary “reply all” messages out of their mailboxes and my own), and I keep my mailing lists up to date.
5. I try to remember that email is a very limited communication device. Those who read my email messages don’t have the benefit of my pitch, tone, inflection, or other non-verbal cues. When in doubt, I make a phone call.
6. I don’t write in ALL CAPS, unless it’s AWESOME or GREAT. Other than praise, nothing should be shouted. The same applies to ?????? or !!!!!!!
7. When I’m angry, I take a walk before I reply. Firing back only creates more heat. If I reply at all, I keep in mind the postcard rule.
8. I use spell-checker.
9. I read my e-mail before I send it. I have created great nonsense by editing parts of a sentence without reading the rest. I have created great nonsense by using cut and paste clumsily. I have created great nonsense by dropping essential letters or entire words. I read my email before I send it.
10. I use “reply all” only when “all” need to know. When Bob sends the minutes of the last meeting to the 15 members of the Board of Directors, I send my “Thanks for the minutes, Bob. Brief and precise as always. thomas” to Bob.
11. I have broken every single one of these ten, but I keep trying.
I have gathered these from multiple sources (google "email etiquette") and modified them for my own use.