This is a common problem and it usually happens when the HTML email was designed or constructed outside of our system using Dreamweaver.  The reason the message does not appear correctly is because it uses embedded style sheet.  Using inline styles will resolve this.

The following pages can be used to compare the formatting of inline styles versus embedded styles:

http://www.quackit.com/css/inline_style_sheets.cfm

http://www.quackit.com/css/embedded_style_sheets.cfm