If you want to create an email, use your email editor, not a piece of document design software. I'm afraid in this case you'll pretty much have to start from scratch with Yahoo's email composer.
Email is not designed for complex document layouts. Yes, you can send email in HTML (web) format, but not all email readers will see this, particularly if they are set to text-only. More and more people are going for text-only, or image-free email, because of the major spam problems associated to HTML email.
You can send your file as an attachment, of course, but in that case it would be best to save it as a PDF, so that more people can read it. You can use
PrimoPDF to convert to PDF format.