If you can’t email something nice, don’t email at all.
Before you send an email, ask yourself if you have written anything that you would not want other people to see. If there is, don’t send it or rewrite it. You know, comments like, “He’s clueless, doesn’t he know that everyone thinks he is an idiot!” or “I just told the boss that Shari is not doing her part – I hope she gets fired!”
Emails are too easy to forward and the chances are high that your harmless venting will end up biting you in the butt. This is particularly the case when forwarding an email to a third person, blasting the person who wrote the first note for their stupidity. The person you wrote to may accidentally hit “reply” on the first note and respond to the person who wrote you by mistake.
And yes, I have learned this one the hard way – more than once – but I’m a little thick.
If you need to vent, do it in person and where you know you cannot be overheard. Or better yet, don’t let little things bother you at all. We are all crazy and stupid at times.