This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma 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.