|There are a few good ways to deal with this type of person, and doing so by email is not one of them. Email is great for communicating facts, figures, data, and straightforward information. When email is used for personal matters or disagreements, you are asking for more trouble.|
When you see email communications morphing from an exchange of data to an exchange of insults, it is time to select another medium. If your antagonist is within walking distance, and it's amazing how many times this is the case, then you should head over to his office for a little discussion. It is guaranteed to be more productive than an online outburst.
If your co-worker is not within walking distance, then you should pick up the phone and give him a call. Although this is not as effective as a face-to-face encounter, it is still closer to real communication than rashly written online words.
When your combative associate realizes that his online assaults are not going to win battles or friends, he is likely to become less interested in dragging you into his virtual war zone.