Your goal when formatting your Ezine should be to service the largest audience possible. To accomplish this, I recommend you publish your Ezine in a simple text format.
Text format is what the majority of the email programs can display properly.
Each line in your Ezine should be between 55 and 60 characters in length. This includes spaces and punctuation. If you go over that amount, many of the email programs will distort your Ezine. I use a free text editor called Edit Pad to keep track of the number of characters per line. If this happens, there are many subscribers who will not open it for fear of viruses.