For those guys trying to extract a message/rfc822 parts correctly here is a hint:
As you may note, if you recurse over the structure object returned by imap_fetchstructure, when you reach the message/rfc822 you find that the message itself counts as a part too, so an attachment in that message should be 2.1.2 (the .1. is the whole rfc822 msg), but if you use that part number in imap_fetchbody you get nothing.
What i did is: my recursing function checks if the part/subtype of a particular part is message/rfc822, and only in that case i do not concatenate the .1 to the part number, because as far as i know, this only happens with this kind of message. And for all the other parts (non rfc822) it concats the dot-partnumber.