For the technical side of HTML email, it's important to realize that you need to do the opposite of all the prevailing trends in web design over the past decade.
Tables should be used for layout, font tags for different typefaces (and sizes, if possible). If you must use CSS, put it inline. No form elements or javascript. And you need to make darn sure that everything looks good without images, because that's how the vast majority of recipients will first see it.
Tables should be used for layout, font tags for different typefaces (and sizes, if possible). If you must use CSS, put it inline. No form elements or javascript. And you need to make darn sure that everything looks good without images, because that's how the vast majority of recipients will first see it.