我正在尝试使用JavaMail以html格式发送电子邮件，但它似乎始终只在Outlook中显示为文本电子邮件。

这是我的代码：

try 
{
    Properties props = System.getProperties();
    props.put("mail.smtp.host", mailserver);
    props.put("mail.smtp.from", fromEmail);
    props.put("mail.smtp.auth", authentication);
    props.put("mail.smtp.port", port);
    Session session = Session.getDefaultInstance(props, null);

    // -- Create a new message --
    MimeMessage message = new MimeMessage(session);

    // -- Set the FROM and TO fields --
    message.setFrom(new InternetAddress(fromEmail, displayName));
    message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to, false));

    MimeMultipart content = new MimeMultipart();
    MimeBodyPart text = new MimeBodyPart();
    MimeBodyPart html = new MimeBodyPart();

    text.setText(textBody);
    text.setHeader("MIME-Version" , "1.0" );
    text.setHeader("Content-Type" , text.getContentType() );

    html.setContent(htmlBody, "text/html");
    html.setHeader("MIME-Version" , "1.0" );
    html.setHeader("Content-Type" , html.getContentType() );

    content.addBodyPart(text);
    content.addBodyPart(html);

    message.setContent( content );
    message.setHeader("MIME-Version" , "1.0" );
    message.setHeader("Content-Type" , content.getContentType() );
    message.setHeader("X-Mailer", "My own custom mailer");

    // -- Set the subject --
    message.setSubject(subject);

    // -- Set some other header information --
    message.setSentDate(new Date());

    // INFO: only SMTP protocol is supported for now...
    Transport transport = session.getTransport("smtp");
    transport.connect(mailserver, username, password);
    message.saveChanges();

    // -- Send the message --
    transport.sendMessage(message, message.getAllRecipients());
    transport.close();

    return true;

} catch (Exception e) {
    LOGGER.error(e.getMessage(), e);
    throw e;
}

有什么想法为什么电子邮件的html版本不会在Outlook中显示？