Content-Type: multipart/mixed; boundary="===============6117237608014356945=="
MIME-Version: 1.0
From: sender@example.com
To: recipient@example.com
Subject: subject

--===============6117237608014356945==
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

this is the body
--===============6117237608014356945==
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: message/rfc822
Content-Disposition: attachment; filename="test.msg"

From: <attachment@example.com>
Subject: écureuil

--===============6117237608014356945==--