Subject: Hello world
From: Test User <test@example.org>
To: Another User <test2@example.org>
Content-Type: multipart/mixed
	boundary="boundary"

--boundary
Content-Type: image/png
Content-Transfer-Encoding: base64
Content-Disposition: ;
        filename="image001.png"
Content-ID: <image001.png@[...]>

aGVsbG8gd29ybGQK
--boundary--