Over 10 years ago I experienced first hand the dangers of using email as a communication tool for managing people. I was confronting someone, let's call him Later Nater, who had promised a deliverable and all I had received was the deafening sound of crickets. This wasn't the first time that Later Nater was late and I had to pick up the slack. So in my frustration I sent a pointed email explaining my frustration at his lack of resolve and dedication to the project. After sending the email, not only did I not feel better, but regretted the way I handled the situation. Afterwards, I met with Nater and he explained how his heart really wasn't in the project and wanted out. Had we sat down early on, we could have resolved the situation before it escalated. As it was, we both left the situation frustrated.
From that point forward I resolved to do my best to not use email as a means of conveying my frustration or disappointment. In my opinion, when we email angry, I find it very similar to road rage. We are detached from the other driver and so we feel right in our actions to cut someone off, honk, or act inappropriately. However, find those same people bump into each other on the street, more often than not they say excuse me and go on their merry way.
When you're feeling your blood start to boil, get out of your chair or pick up the phone. If you must write the email, save it in your drafts and send it the next morning when the dust has settled.