The Received header (and all of the headers that follow it) are not part of the MIME part headers - they are the content of the MIME part.
This attachment has a MIME-type of message/rfc822 which is an email message. When you parse the content of the MIME part (which starts with the Received header), what you end up with is another message object.
The Received header (and all of the headers that follow it) are not part of the MIME part headers - they are the content of the MIME part.
This attachment has a MIME-type of message/rfc822 which is an email message. When you parse the content of the MIME part (which starts with the Received header), what you end up with is another message object.