From: Some One <someone@example.com>
MIME-Version: 1.0
Content-Type: multipart/mixed;
        boundary="+Testboundary text"

This is a multipart message in MIME format.

--+Testboundary text
Content-Type: multipart/alternative;
        boundary="hello, boundary"

--hello, boundary
Content-Type: text/plain

this is the body text

--hello, boundary
Content-Type: text/html;
       charset="utf-8"
Content-Transfer-Encoding: quoted-printable

<font color=3D"#FF0000">This is the body text</font>

--hello, boundary--
--+Testboundary text
Content-Type: text/plain;
Content-Disposition: attachment;
        filename="test.txt"
Content-Transfer-Encoding: base64

dGhpcyBpcyB0aGUgYXR0YWNobWVudCB0ZXh0

--+Testboundary text--
Some additional content here.