You've probably noticed that the majority of email newsletters you receive these days are designed with a fixed width as opposed to a fluid layout.
This is because the majority of email clients and web-based email providers don't use the full width of your screen to display an email message. Whether it's ads on Gmail, a menu in Hotmail or your Inbox in Outlook, a chunk of screen real estate is often already being used.
Remember, your recipients are busy and impatient, so horizontal scroll bars are even more of a no-no in email than a web page.
Because of this, it is a good idea to keep your emails to a fixed width of no more than 550-600 pixels. This should ensure that in most cases, your subscribers can view your email as you intended.
What about height?
Obviously the height of each email you send will vary depending on the amount of content. At the same time, it's good to keep in mind that a lot of your recipients may scan your email in a preview pane before they decide to read the entire thing.
The average preview pane is around 300-500 pixels high, so make sure you include any important bits of your email in this area. First impressions count.