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.