[Zope] HTML/PlainText alternate eMails from Zope

Hello, I want to send eMail from Zope that automatically shows HTML to HTML-enabled eMail clients and PlainText otherwise. It seems to concern a boundary of type? alternate. I'm not very versed in eMail and its protocols. I was hoping one of the DTML sendmail options would achieve this. Anyone know how to do this? Or some keywords for Google other than HTML eMail boundary or alternate? Thanks, Jon Cyr cyrj@cyr.info