When you take a look at http://www.campaignmonitor.com/css/ you learn that you need to embed inline styles in your HTML, in order for your email to be read in any mail client.
Do you know any tools or script to automatically convert an HTML file with a declared in to an HTML file with only inline CCS style attributes ?
Edit: Any Javascript solution ( ie: http://www.robertnyman.com/2006/04/24/get-the-rendered-style-of-an-element/ ) ? With jQuery ?
Check the premailer.dialect.ca online converter or this Python script to do it.