From: aperson@dom.ain
To: bperson@dom.ain
Content-Type: multipart/digest; boundary=XYZ
--XYZ
Content-Type: text/plain
This is a text plain part that is counter to recommended practice in
RFC 2046, $5.1.5, but is not illegal
--XYZ
From: cperson@dom.ain
To: dperson@dom.ain
A submessage
--XYZ--