However, now that you've got an HTML file, you've still got to convert it to the email version of HTML, which is not the same. The problem happens when you want to embed images or objects.
How do you plan to send the email? Regular client? Bulk mailer? Custom mailer? That's the tricky part.
I'd suggest getting the HTML into a GOOD bulk mailer and then going through and attaching all the images again to make sure they are properly embedded. Then send yourself a test to check. Use a regular client and a web based email account. You may also wish to check with a text client like Pine or Elm. (Most good mailers give you an option to also have a text only version - which is a part of the email RFC.)
Good luck