The hybrid format email is considered as a junk email (or spam)in Apple Mail 4.4

Question

In Mac OSX 10.6.6, When I use Apple Mail 4.4 to receive the hybrid format email( include HTML and Text format in one email), the Apple Mail 4.4 will be think this email is a junk email.
Is this a bug for the Mail 4.4? Anybody can help to resolve this issue?
FYI, The following is my JAVA code for how to send a hybrid format email:
msg.setSubject("test");//set subject
MimeBodyPart mbp1 = new MimeBodyPart();
mbp1.setContent("test", "text/plain; charset=utf-8");//set text format content
MimeBodyPart mbp2 = new MimeBodyPart();
mbp2.setContent("test", "text/html; charset=utf-8");//set HTML format content
Multipart mp = new MimeMultipart("alternative");
mp.addBodyPart(mbp1);//add text content
mp.addBodyPart(mbp2);//add HTML content
msg.setContent(mp);
Transport.send(msg);//send email

Answer 1

Sorry to be slow to respond -- had a doctor appointment, and also had to hunt up a boot volume with 10.6.6 and Mail 4.4 on it, just to be sure.
Your test message was not perceived as SPAM/Junk at all.  Not when received in Mail 4.5, Mail 4.4, nor Mail 2.1.3 in Tiger.
Nothing about the Long Headers indicated anything suspicious.  The headers I was looking primarily at are pasted below, and do reveal anything private.  These the result of the filters on my incoming server:
X_Cmae_Category:   0,0 Undefined,Undefined
          X-Cnfs-Analysis:   v=1.1 cv=JQNK39t9F4kLyjfJz/k8C0DfBhSrK9xA1Y4SBRwEmYU= c=1 sm=0 a=BLceEmwcHowA:10 a=1FzqG5ILVBdwvA7Y_sMA:9 a=QEXdDO2ut3YA:10 a=qIwwZl7lo8ZhrKw95CmXbg==:117
  X-Cm-Score:           0
          X-Scanned-By:   Cloudmark Authority Engine
          Authentication-Results:   mx01.insight.synacor.com header.from=[email protected]; sender-id=neutral
          Authentication-Results:   mx01.insight.synacor.com smtp.mail=[email protected]; spf=neutral; sender-id=neutral
          Received-Spf:   neutral (mx01.insight.synacor.com: 74.128.0.95 is neither permitted nor denied by domain of zone1.dev.hf.webex.com)
  X-Ironport-Anti-Spam-Filtered:           true
          X-Ironport-Anti-Spam-Result:   As0IAEyBx009vxsiTmdsb2JhbACEUqE6AQEiSYhqqnGPfoUKgQIEhj6NTx2KJQ
          X-Ironport-Av:   E=Sophos;i="4.64,338,1301889600";  d="scan'208";a="381038056"
  X-Connecting-Ip:           61.191.27.34
          Message-Id:   <27817788.01304920419178.JavaMail.Ma.Jin@majin-work>
  Mime-Version:           1.0
          Content-Type:   multipart/alternative;  boundary="----=_Part_0_24435002.1304920419147"