(header)
Content-Type: multipart/mixed;
boundary="----=_NextPart_000_AAAAA"

(body)
This is a multi-part message in MIME format.

------=_NextPart_000_AAAAA
Content-Type: multipart/alternative;
boundary="----=_NextPart_001_BBBBB"

     ------=_NextPart_001_BBBBB
     Content-Type: text/plain;

     Plain Text Message Here

     ------=_NextPart_001_BBBBB
     Content-Type: text/html;

     <B>HTML Message Here</B><br>

     ------=_NextPart_001_BBBBB--

------=_NextPart_000_AAAAA
Content-Type: application/msword; name="test.doc"
Content-Transfer-Encoding: base64