This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
If you downloaded JavaMail then you have a "demo" directory that contains example code. You will find an example of what you want to do in that directory, I think. You need separate parts for your body text and each of your attachments.