Use one of the Insert steps with the $Path variable to insert it into the container field as part of this same script.
Emails from FileMaker are plain text. I'm surprised that you get any HTML features at all form the email. You may want to investigate the use of an email plug in that support HTML formatting.
I thought I had tried this but discovered I was in the wrong layout so it did not post. Have it working now.
And yes, try it. If you leave the message field blank, the email is inserted into outlook in HTML format.