Multipart Messages Can Be Nested
From: Nathaniel Borenstein <nsb@bellcore.com>
To: Ned Freed <ned@innosoft.com>
Content-type: multipart/mixed; boundary="boundary 1"
This is the first part of a multipart message
Content-type: multipart/mixed; boundary=“boundary 2”
This is a nested part with its own boundary parameter.
There could be anything in here.
Here is another message part