Javamail Content-Type - image

Question

I'm trying to send an Email via javamail adding embedded Images and an Outlook Invation which should be displayed showing up the buttons to accept/decline .... To make the buttons show up, i have to set the Content-Type of the MimeMultipart to related.
MimeMultipart multipart = new MimeMultipart("related");
Once this is done, the embedded Pictures wont show up again.
To Display the embedded images it should be alternative.
I have send myself a Mail from Outlook containing an Image as well as a invation to a meeting.
When I check the header there, it says:
Content-Type: multipart/related;
boundary="_005_CCF531A072806F489D02A6DD2CF322A01D88EEA2de35s004hst42wp_";
type="multipart/alternative"
I have already tried to set the Content-Type adding Parameters (type, charset ...) but it seems like their just getting ignored when sending the message. Here is the Method which I am calling to create the Message Part:
private Message generateMessage() throws Exception
{
Configuration conf = Configuration.getInstance();
// Get system properties
Properties props = System.getProperties();
// Setup mail server
props.put("mail.smtp.host", conf.getProperty(Configuration.MAIL_SERVER));
// Get session
Session session = Session.getDefaultInstance(props, null);
// Create the message
Message message = new MimeMessage(session);
// Fill its headers
message.setSubject(this.subject);
message.setFrom(new InternetAddress(fromEmail));
Address[] replyTo = new Address[]{new InternetAddress(replyEmail)};
message.setReplyTo(replyTo);
// Create a related multi-part to combine the parts
MimeMultipart multipart = new MimeMultipart("related");
// Create your new message part
BodyPart messageBodyPart = new MimeBodyPart();
multipart.addBodyPart(messageBodyPart);
// ADD IMAGES
multipart = attachImages(multipart);
// ADD CALENDAR-FILE
multipart = attachCalendarFile(multipart);
// Set Content-Type
ContentType ct = new ContentType(message.getContentType());
ct.setParameter("charset", "utf-8");
ct.setParameter("type", "multipart/alternative");
// Set Multipart-Content to Message including the Content-Type
message.setContent(multipart, ct.toString());
return message;
}
The output of message.writeTo(System.out); is the following:
From: mail#sender.com
Reply-To: noreply#recipient.com
Message-ID: <1150322817.1.1397725164700.JavaMail.User#MacBooks-mailserver.local>
Subject: test
MIME-Version: 1.0
Content-Type: multipart/related;
boundary="----=_Part_0_72769750.1397725164655"
------=_Part_0_72769750.1397725164655
Is there any chance to make it work with embedded images AND invations?
Thanks in advance!

Answer 1

There's three types of multiparts, each used for a different purpose. In some cases you might need to use all three. For example, a message with a calendar attachment, html content using images, and equivalent plain text content, might have a structure such as this:
multipart/mixed
multipart/alternative
text/plain
multipart/related
text/html
image/jpeg
text/calendar

Answer 2

Google search led me here, so for future searchers:
#bill-shannon is of course correct. However, please save yourself the trouble of figuring out the low level Mime RFC stuff, and just use something like Simple Java Mail (open source) which figures out which structure suits best based on the input you provide. You can interactively explore all the possible structures Simple Java Mail can come up with. Disclaimer: I maintain this library (but I actually came across this SO question in my research into including voting buttons in emails for Outlook :) )
In your case you would use the following. First produce a Calendar content string, using something like ical4j:
Calendar icsCalendar = new Calendar();
icsCalendar.getProperties().add(new ProdId("-//Events Calendar//iCal4j 1.0//EN"));
icsCalendar.getProperties().add(Version.VERSION_2_0);
(..) // add attendees, organizer, end/start date and whatever else you need
// Produce calendar string
ByteArrayOutputStream bOutStream = new ByteArrayOutputStream();
new CalendarOutputter().output(icsCalendar, bOutStream);
String yourICalEventString = bOutStream.toString("UTF-8")
Then use Simple Java Mail's email builder to set the Calendar content alongside everything else such as images:
Email email = EmailBuilder
.startingBlank()
.withCalendarText(CalendarMethod.REQUEST, yourICalEventString)
.everythingElseLikeImagesHeadersAttachmentsEtcEtc()
.buildEmail();
Then send using the mailer builder:
MailerBuilder
.withSMTPServer("server", 25, "username", "password")
.buildMailer()
.sendMail(email);
Then depending on whether you provided text, html attachments or other things, Simple Java Mail will select the appropriate Mime structure with mixed/related/alternative parts.