Subject: multipart/alternative wrapping a multipart/related html part
From: root@localhost
To: rt@example.com
Content-Type: multipart/alternative; boundary="=_alt_boundary"

This is a multipart message in MIME format.

--=_alt_boundary
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit

PLAINDOWNGRADEMARKER this is the plain-text downgrade of the rich message.

--=_alt_boundary
Content-Type: multipart/related; boundary="=_rel_boundary"

--=_rel_boundary
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: 7bit

<div>HTMLBODYMARKER this is the composed rich body.<br />
<img src="cid:inline-image@example.com" /></div>

--=_rel_boundary
Content-Type: image/png; name="inline.png"
Content-Transfer-Encoding: base64
Content-Disposition: inline; filename="inline.png"
Content-ID: <inline-image@example.com>

iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+M8A
AAMBAQDJ/pLvAAAAAElFTkSuQmCC

--=_rel_boundary--

--=_alt_boundary--
