The 'Incoming Mail Width' option allows you to customize the width of the text box displaying messages for all the incoming mail.
Click the 'Incoming Mail Width' drop-down box to select the width in pixels of the mail message text box and click the 'Update Information' button. You have choices ranging from 60 to 130 pixels wide. If you select 70 pixels the messages you receive in your inbox when being read will be formatted in a non-editable text box in such a way that each line will be 70 pixels wide. You also have the option of not wrapping the text to a fixed width. This will display the entire message you receive in a single line without any restriction on its width.