why the smime encrypted letter always decoded as Attachment in outlook?

"wooce" <[email protected]> Tue, 18 Jun 2002 19:45:03 -0700
Newsgroups	gmane.ietf.sfl
Message-ID	<[email protected]>
below is the smime encrypted letter I created using the SFL  library.   
MIME-Version: 1.0
Message-Id: <3D0F032A.000001.14739@wolfie>
Date: Tue, 18 Jun 2002 17:53:46 +0800 (CST)
From: [email protected]
To: [email protected]
Subject: test
Content-Type: Application/x-pkcs7-mime;
 smime-type=enveloped-data;
 boundary="------------Boundary-00=_MHBW40MWKGMMYJ0CCJD0";
 name="smime.p7m"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="smime.p7m"
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but when I open it in MS Outlook,  it always be decoded as a letter with an attachment which content is as below, although I can still 
see the original letter content in the attachment,  it's not what I want.  While I use the Outlook itself 
to create the encrypted letter and then open it again in Outlook,  it  give the original content directly in the main mail body and has no an attachment that had to be
opened.
how I can make the encrypted smime letter by SFL library be decoded bye MS Outlook as this style?     (I create the letter using wooce.pfx in attachment, password is 123456)

From: [email protected]
To: [email protected]
Subject: test
Date: Tue, 18 Jun 2002 17:53:46 +0800 (CST)
Content-Type: Multipart/Alternative;
  boundary="------------Boundary-00=_MHBW40MWKGMMYJ0CCJD0"


--------------Boundary-00=_MHBW40MWKGMMYJ0CCJD0
Content-Type: Text/Plain
Content-Transfer-Encoding: 7bit

haha
--------------Boundary-00=_MHBW40MWKGMMYJ0CCJD0
Content-Type: Text/HTML
Content-Transfer-Encoding: 7bit

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><HTML><HEAD><META http-equiv=3DContent-Type content=3D"text/html; charset=3Dgb2312"><META content=3D"MSHTML 6.00.2715.400" name=3DGENERATOR><STYLE></STYLE></HEAD><BODY bgColor=3D#ffffff><DIV><FONT face=3DArial size=3D2>haha</FONT></DIV></BODY></HTML>
--------------Boundary-00=_MHBW40MWKGMMYJ0CCJD0--
wooce.pfx (application/x-pkcs12, 3.9 KB) - not displayed