Problem sending a mail to many adresses with attachments (Javamail, JSP)

Question

Hi,
i got a problem with JavaMail trying to send a mail to different email-adresses in a JSP. The mail should be send to about 27 adresses, which works fine whenever i send it without any attachments. As soon as i attach a file, the mail still gets send without an error, but only to about 12 adresses instead of the intended 27. I get the adresses out of a database and in either case, there ist the correct amount of adresses. The Mailserver doesnt report anything - it sends the mails without any problem at the 12 adresses.
Here is the part of the code, thats sending:
Properties props = new Properties();
props.put("mail.smtp.host", "192.168.1.1 ");
Session s;
MimeMessage message;
InternetAddress from = new InternetAddress("[email protected]");
InternetAddress to;
s = Session.getInstance(props,null);
Transport trans=s.getTransport("smtp");
//get adresses from db
while (rspartner.next())
     to = new InternetAddress(rspartner.getString("postfach"));
     message.addRecipient(Message.RecipientType.TO, to);
     empfaengerzeile=rspartner.getRow();
     //out.println(empfaengerzeile+" --- "+rspartner.getString("postfach")+"<br>");
     BodyPart messageBodyPart=new MimeBodyPart();
     messageBodyPart.setText(nachricht);
     Multipart multipart=new MimeMultipart();
     multipart.addBodyPart(messageBodyPart);
     //Dateinamen und Speicherort des Plan ermitteln
     queryAnhang=dbCon.prepareStatement("select pfad from m_baukoord_kommentar where baukoord_id=? and titel='Entwurfsplan'");
     queryAnhang.setString(1,request.getParameter("projektid"));
     rsanhang=queryAnhang.executeQuery();
     rsanhang.next();
     datei=rsanhang.getString("pfad");
     //Datei zippen
     quellpfad+= ebaukonr.trim() + "/" + datei;
     if(datei.contains("."))
          zipfilename=datei.substring(0,datei.lastIndexOf('.'))+".zip";
     else
          zipfilename=datei+".zip";
     zielpfad=config.getServletContext().getRealPath("")+"/strasse/UserDownloads/" + zipfilename;
     ZipOutputStream zipout = new ZipOutputStream(new FileOutputStream(zielpfad));
     zipout.setLevel(9);
     zipout.setMethod(ZipOutputStream.DEFLATED);
     FileInputStream in = new FileInputStream(quellpfad);
     zipout.putNextEntry(new ZipEntry(datei));
     int len;
     while ((len = in.read(buf)) > 0) {
         zipout.write(buf, 0, len);
     zipout.closeEntry();
     in.close();     
     zipout.close();
     //Datei anhaengen
     messageBodyPart = new MimeBodyPart();
     FileDataSource source = new FileDataSource(zielpfad);
     messageBodyPart.setDataHandler(new DataHandler(source));
     messageBodyPart.setFileName("Entwurfsplan.zip");
     multipart.addBodyPart(messageBodyPart);
     message.setSubject("Neues Projekt " + titel + " verfügbar");
     message.setContent(multipart);
     trans.send(message);

Answer 1

With active debug i got following information:
The first mail in the debug-log is with the source code as quoted in my first post, the second mail is when i cut out the part which generates and adds the attachement. I had to make the adresses anonymous, but the second mail contains a lot more adresses then the first, although they both use the same query with same parameters, etc.
Have i done something wrong with the attachements? Overwriting headers, syntax errors, anything? I'm out of ideas...
edit: Had to cut out the debug-log because it is too big. It just said that everything was working ok, but the first mail contains too few adresses and the second (without attachement) the correct number of adresses. I can mail the log, if you like.