ref: 4bb9e229bcb23826a0fde907667c8fd6565d98d2
dir: /sys/lib/python/email/test/data/msg_42.txt/
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--