From user@domain  Fri Feb 22 17:06:23 2008
From: user@domain.org
Date: Sat, 24 Mar 2007 23:00:00 +0200
Mime-Version: 1.0
Content-Type: message/rfc822

From: sub@domain.org
Date: Sun, 12 Aug 2012 12:34:56 +0300
Subject: submsg
Content-Type: multipart/digest; boundary="foo"

prologue

--foo 
Content-Type: message/rfc822

From: m1@example.com
Subject: m1

m1 body

--foo 
Content-Type: message/rfc822
X-Mime: m2 header

From: m2@example.com
Subject: m2

m2 body

--foo--

epilogue