How to put Image in mail's header(Spring Boot)?

Question

I am developing an app where I need to set image in a header and footer of a mail. I saw method setHeader(String header-name, String header_value) but when I put into it a path to my image I don't get anything. This is my code:

public static void send(String host, String port,
            final String userName, final String password, String toAddress,
            String subject, String htmlBody,
            Map<String, String> mapInlineImages)
                throws AddressException, MessagingException {
        // sets SMTP server properties
        Properties properties = new Properties();
        properties.put("mail.smtp.host", host);
        properties.put("mail.smtp.port", port);
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.starttls.enable", "true");
        properties.put("mail.user", userName);
        properties.put("mail.password", password);
 
        // creates a new session with an authenticator
        Authenticator auth = new Authenticator() {
            public PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(userName, password);
            }
        };
        Session session = Session.getInstance(properties, auth);
 
        // creates a new e-mail message
        Message msg = new MimeMessage(session);
 
        msg.setFrom(new InternetAddress(userName));
        InternetAddress[] toAddresses = { new InternetAddress(toAddress) };
        msg.setRecipients(Message.RecipientType.TO, toAddresses);
        msg.setSubject(subject);
        msg.setSentDate(new Date());
        msg.setHeader("image1", "D:\\broki\\src\\main\\resources\\imageHeader.jpg");
 
        // creates message part
        MimeBodyPart messageBodyPart = new MimeBodyPart();
        messageBodyPart.setContent(htmlBody, "text/html");
 
        // creates multi-part
        Multipart multipart = new MimeMultipart();
        multipart.addBodyPart(messageBodyPart);
 
        // adds inline image attachments
        if (mapInlineImages != null && mapInlineImages.size() > 0) {
            Set<String> setImageID = mapInlineImages.keySet();
             
            for (String contentId : setImageID) {
                MimeBodyPart imagePart = new MimeBodyPart();
                imagePart.setHeader("Content-ID", "<" + contentId + ">");
                imagePart.setDisposition(MimeBodyPart.INLINE);
                 
                String imageFilePath = mapInlineImages.get(contentId);
                try {
                    imagePart.attachFile(imageFilePath);
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
 
                multipart.addBodyPart(imagePart);
            }
        }
 
        msg.setContent(multipart);
 
        Transport.send(msg);
    }
}

As you can see in part

msg.setHeader("image1", "D:\\broki\\src\\main\\resources\\imageHeader.jpg")

I put some key and value which is path to my Image which I want to set into header. But nothing happens. Can someone help me?

Answer 1

The word "header" in a MIME message refers to a section of the message that has "key: value" fields. This section is called "header" because it's transmitted before the "body" content of the message. The headers are for things like "Date", "Subject", "Content-Type".

The word "header" does not refer to a graphical header that would be visible on the screen or when printed. To add this type of a header, you have to modify the content of the message. In your program, that's stored in the htmlBody variable.

I don't think you can simply modify htmlBody to add a header to it, without knowing how it is structured. In the general case, the page header has to be incorporated in the HTML message design from the start.