It took me a while to figure out how part id's(numbers) are assigned to different parts of a message.  After getting a few AOL e-mails that had a semi-complex structure I was finally able to break it down. 

0 multipart/mixed
    1 multipart/alternative
        1.1 text/plain
        1.2 text/html
    2 message/rfc822
        2 multipart/mixed
            2.1 multipart/alternative
                2.1.1 text/plain
                2.1.2 text/html
            2.2 message/rfc822
                2.2 multipart/alternative
                    2.2.1 text/plain
                    2.2.2 text/html

Hopefully this will help others get the different body parts of a message.