Update: Gmail made some changes in late 2016 to support CSS styles in the header. Inlining is still a good idea, though, since other email clients may still strip style tags.
One of the more peculiar frustrations of email development is that many email clients strip out the data in your head tag. This means your CSS has to be written inline in a style tag to make sure your emails look fabulous in all clients.
“But,” you may be thinking, “that doesn’t sound very cascading at all!” And you would be right.
In fact, it’s so fine we want to do something nice for you, so we’ve made our CSS Inliner available for everyone – you don’t even have to log in.
Finally, anyone can achieve their dreams of turning this: