Gosh, I hope I never make this mistake again. A few years ago, I sent a smart aleck e-mail about an irritating co-worker to a friend and actually sent it to the irritating one instead. It felt good for a second to send that e-mail but it took many days for the embarassment to wear off every time I passed him in the hall. So I now 1) at least look twice at the to category or more importantly 2) don't send those types of e-mails anymore. So here are a few other things I've learned:
* Use good grammar. Make it easier for any recipient to read your message. No capitalization, bad punctuation, missing words slows the reader down.
* Take a break when you receive a stinging message. Maybe the sender didn't mean it the way it came across. Respond with just the facts or better yet, go talk to them in person.
* Don't write in all caps. Ever.
* Keep font easy to read.
* Try not to reply all to everyone if only one person needs to know.
* De-tweak the tweaking cc. You can cc the boss every time somebody doesn't "do right." Your boss will appreciate it in the beginning. But when your co-workers hesitate about talking with you or worse, working with you, you lose.
Here are two articles with tips.
Top 20 Rules of Most Important Rules of E-mail Ettiquette
What are your thoughts on e-mail rules?