Here's how you use JavaMail in a Netscape 4.x applet

Question

First of all... Sun has said that they are working on patching JavaMail for the next minor release so that it will be usable with Netscape.
But for those with itchy pants... here's how you do to send mail from a Netscape 4.x applet without using the Java Plug-in.
First of all... you'll need to sign the applet. Now I'm not so good with singing tools so I don't know if Netscape 4.x allows using Sun's signing tools. I used Netscapes own "signtool" just to be sure.
You'll need to unjar activation.jar and mail.jar (or mailapi.jar plus smtp.jar). Use signtool to sign and jar your own classfiles plus those from the jar-files mentioned.
This creates a small problem though: atcivation.jar and mail.jar has files in the META-INF directory. Netscapes signtool ignores these files. So you'll have to patch around that.
Using the "sendfile.java" demo as basis... here's how you deal with the missing configuration files.
    // You'll have to request this privilige or Netscape will bolt on you.
    // If you need cross-platfor compatibility you'll need to wrap this up or IE
    // will be really cranky at this. Try by doing something you know
    // IE accepts but that Netscape don't. Catch the  exception as just an
    // Exception and do the following in the catch.
    try {
      PrivilegeManager.enablePrivilege("UniversalPropertyRead");
    } catch (netscape.security.ForbiddenTargetException e2) {
      System.out.println("Failed! Permission to read system properties denied by user.");
    } catch (Exception e2) {
      System.out.println("Failed! Unknown exception while enabling privilege.");
      e2.printStackTrace(System.out);
    // create some properties and get the default Session
    Properties props = null;
    props = System.getProperties();
    props.put("mail.smtp.host", mailhost);
    // The mailcap command map needs a missing
    // config file. So you'll have to hardwire the different
    // commands like this.
    javax.activation.MailcapCommandMap commandMap = new javax.activation.MailcapCommandMap();
    commandMap.addMailcap("text/plain;;          x-java-content-handler=com.sun.mail.handlers.text_plain");
    commandMap.addMailcap("text/html;;          x-java-content-handler=com.sun.mail.handlers.text_html");
    commandMap.addMailcap("text/xml;;          x-java-content-handler=com.sun.mail.handlers.text_xml");
    commandMap.addMailcap("multipart/*;;          x-java-content-handler=com.sun.mail.handlers.multipart_mixed");
    commandMap.addMailcap("message/rfc822;;     x-java-content-handler=com.sun.mail.handlers.message_rfc822");
    commandMap.addMailcap("image/gif;;          x-java-view=com.sun.activation.viewers.ImageViewer");
    commandMap.addMailcap("image/jpeg;;          x-java-view=com.sun.activation.viewers.ImageViewer");
    commandMap.addMailcap("text/*;;          x-java-view=com.sun.activation.viewers.TextViewer");
    commandMap.addMailcap("text/*;;          x-java-edit=com.sun.activation.viewers.TextEditor");
    javax.activation.MailcapCommandMap.setDefaultCommandMap(commandMap);
    // Now here is a really weird thing. This class - MimeUtility - will
    // be used later on. But the ClassLoader in Netscape seems
    // to be broken. I downloaded J2EE and fiddled with this class a bit.
    // It seems that the following line will get you around this problem.
    Object o = MimeUtility.class;
    try {
      // create a message
      Session session = Session.getDefaultInstance(props, null);
      session.setDebug(true);
      MimeMessage msg = new MimeMessage(session);
      msg.setFrom(new InternetAddress(from));
      InternetAddress[] address = {new InternetAddress(to)};
      msg.setRecipients(Message.RecipientType.TO, address);
      msg.setSubject("Message from scratchpad");
      // create and fill the first message part
      MimeBodyPart mbp1 = new MimeBodyPart();
      mbp1.setText(message);
      // create the second message part
      MimeBodyPart mbp2 = new MimeBodyPart();
      // attach the file to the message
      // This is not the same as the original.
      // The ByteArrayDataSource class helps you attach an arbitrary file-type.
      // The code for that is found here:
      // http://forums.java.sun.com/thread.jsp?forum=43&thread=73819
      DataSource ds = new ByteArrayDataSource(imageData, "image/gif", "image.gif");
      mbp2.setDataHandler(new DataHandler(ds));
      mbp2.setFileName("image.gif");
      // create the Multipart and its parts to it
      Multipart mp = new MimeMultipart();
      mp.addBodyPart(mbp1);
      mp.addBodyPart(mbp2);
      // add the Multipart to the message
      msg.setContent(mp);
      // set the Date: header
      msg.setSentDate(new Date());
      // send the message
      // Transport.send() will give you exception in Netscape.
      // Here is how you do what that method does.
      msg.saveChanges();
      com.sun.mail.smtp.SMTPTransport transport = new com.sun.mail.smtp.SMTPTransport(session, null);
      transport.connect();
      transport.sendMessage(msg, address);
      transport.close();     
    catch (MessagingException mex) {
      mex.printStackTrace();
      Exception ex = null;
      if ((ex = mex.getNextException()) != null) {
        ex.printStackTrace();
    }Enjoy
/Michael

Answer 1

Typical... i knew I'd fumble. There is one more thing you need to do.
Download J2EE, source code edition and patch the file javax.mail.internet.MimeUtility.java
Change the line
InputStream is = javax.mail.internet.MimeUtility.class.getResourceAsStream("/META-INF/javamail.charset.map");...to...
InputStream is = javax.mail.internet.MimeUtility.class.getResourceAsStream("/javamail.charset.map");Also, after you unjar the jarfiles and before you run the signtool, move the file META-INF/javamail.charset.map to the partent of the META-INF directory.
/Michael