Sending HTML email using javax.mail fails on Google App Engine

Question

In summary I am trying to send HTML emails on a google app engine application using javax.mail. The structure that I want for the email is:

• Alternative
  • Text
  • Related
    • HTML
    • Image

However when I try to build and send an email using this structure it fails on google app engine. One issue in particular was that no matter what the structure was I was not able to embed a multipart inside of another multipart and send that email on google app engine.

I have tried building and sending emails using this structure outside of the google app engine application using a smtp server and it works fine. However, migrating that same code to my real application fails to work.

I should note that I am able to send emails on the google app engine that are plain text or only html but when I try to add together all these pieces to compose a full email it fails.

  Message msg = new MimeMessage(session);

  Multipart multiPart = new MimeMultipart("alternative");
  Multipart relatedMp = new MimeMultipart("related");

  BodyPart txtBdp = new MimeBodyPart();
  txtBdp.setContent(msgBody, "text/plain");
  multiPart.addBodyPart(txtBdp);

  BodyPart htmlBdp = new MimeBodyPart();
  htmlBdp.setContent(htmlBody, "text/html");
  relatedMp.addBodyPart(htmlBdp);

  DataSource dataSrc = new FileDataSource(new File(imageFileNm));

  BodyPart imageBdp = new MimeBodyPart();
  imageBdp.setDataHandler(new DataHandler(dataSrc));
  imageBdp.setFileName("logo.png");
  imageBdp.setHeader("Content-ID", "<image_logo>");
  imageBdp.setDisposition(MimeBodyPart.INLINE);
  relatedMp.addBodyPart(imageBdp);

  BodyPart relatedBdp = new MimeBodyPart();
  relatedBdp.setContent(relatedMp);
  multiPart.addBodyPart(relatedBdp);

  msg.setFrom(new InternetAddress(emailAddr));
  msg.addRecipient(Message.RecipientType.TO, new InternetAddress(emailAddr, recipientNm));
  msg.setSubject(subject);
  msg.setContent(multiPart);
  msg.saveChanges();

  Transport.send(msg);

The error message I am getting is:

Attachment needs content and name com.google.appengine.api.mail.MailService$Attachment.(MailService.java:56) com.google.appengine.api.mail.stdimpl.GMTransport.convertAttachments(GMTransport.java:334) com.google.appengine.api.mail.stdimpl.GMTransport.convertAttachments(GMTransport.java:321) com.google.appengine.api.mail.stdimpl.GMTransport.convertAttachments(GMTransport.java:295) com.google.appengine.api.mail.stdimpl.GMTransport.sendMessage(GMTransport.java:262) javax.mail.Transport.send(Transport.java:95) javax.mail.Transport.send(Transport.java:48)

I'm not sure why this code fails when I run it on google app engine considering that I am using the correct name format for the email from which to send it, and that it works outside of google app engine.