Content-Type: multipart/mixed; boundary="AAA"

From: Mail Delivery Subsystem <xxx@example.com>

To: yyy@example.com



This is a MIME-encapsulated message



--AAA



Stuff



--AAA

Content-Type: message/rfc822



From: webmaster@python.org

To: zzz@example.com

Content-Type: multipart/mixed; boundary="BBB"



--BBB--



--AAA--

