Another fun fact about email
CSS has to be inlined for your styles to work reliably. Remember the good old days of FrontPage? Yea, like that.
<span style="font-size: 18px;">
...
</span>
Gross! But luckily there are a lot of tools that will take your normal CSS classes and inline them for you. Both frameworks from yesterdays post have methods for inlining.
I use Premailer-rails for Ruby on Rails projects.