The fun world of HTML

I've been creating HTML, off and on, for more than 7 years now, and thought I had a reasonable grasp of it. Today though, I've been defeated in the process of trying to send out an email containing an existing HTML file, compete with CSS. It more or less works, but the CSS information doesn't get through. I've sent out an SOS, so hope to have the answer in a day or so.

I could just create it in the email client, but want to do this as a monthly newsletter, so will work from an HTML template (at least, that's the plan).

Think I'll go and read the book du jour.