How do I send a binary attachment in an email with Java using the JavaMail API?

MimeMultipart messageContent = new MimeMultipart();

BodyPart bodyPart = new MimeBodyPart();
DataSource source = new FileDataSource(yourFile);
bodyPart.setDataHandler(new DataHandler(source);
bodyPart.setFileName("MyFile.ext");
bodyPart.setDisposition(Part.ATTACHMENT);

// Then add to your message:
messageContent.addBodyPart(bodyPart);