A client recently asked why e-mail newsletters are often laid out in a rather narrow format. An e-newsletter should be formatted for a maximum of 600 pixels wide, while the most popular screen resolution is 1280 pixels wide. Why don't they take advantage of modern, higher resolution monitors? This was our reply:

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The main reason is to prevent left-right scrolling in the viewing window—a real annoyance for readers. There is a huge variety in e-mail readers out there: Outlook, Thunderbird, Outlook Express, and Eudora, to name a few; web based e-mail programs, such as Hotmail and Gmail; webmail viewers on company intranets; and e-mail readers on smart phones. A good e-news designer must design for all eventualities—never assume that recipients have their browser/e-mail client window set to full screen; so the open window could be almost any size. Also, allowances need to be made for sidebars within that browser window.