HTML and Text emails

Howdy, I've noticed that a number of online marketing companies now advertise the ability to send a combined HTML and Text email. The text email readers then apparently display these as text, and html email readers display these as html. I know how to send an html email, and a text email. But I can't figure out how you would send a combined html and text email. Could anybody give me an idea of how this would work, or perhaps point me the way to a tutorial or article? The tutorial doesn't have to be specifically for PHP -- once I know how it works, I can adapt it to PHP myself! Many Thanks! Rita Mikusch __________________________________________________ Do You Yahoo!? LAUNCH - Your Yahoo! Music Experience http://launch.yahoo.com