How to Support S/MIME using java mail.

Question

Hi All,

I want to send S/MIME to encrypt messages while sending with UI I am getting an error:

I am using the below code it sends an attachment that I am not able to access and gives the error:

KeyStore keystore = KeyStore.getInstance("PKCS12");
        FileInputStream fis = new FileInputStream("path/keystore.p12");
        keystore.load(fis, "p12password".toCharArray());
        PrivateKey privateKey = (PrivateKey) keystore.getKey("myalias", "p12password".toCharArray());
        Certificate cert = keystore.getCertificate("myalias");
        Certificate recipientCert = keystore.getCertificate("myalias");  // Recipient's certificate
        // Set up the session
        Properties props = new Properties();
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.starttls.enable", "true");
        props.put("mail.smtp.host", host);
        props.put("mail.smtp.port", "587");
        Session session = Session.getInstance(props, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });
        // Create the message to be encrypted
        MimeBodyPart messageBodyPart = new MimeBodyPart();
        messageBodyPart.setText("This is an encrypted email using S/MIME.");
        // Create an encrypted message part using SMIMEEnvelopedGenerator
        SMIMEEnvelopedGenerator envGen = new SMIMEEnvelopedGenerator();
        envGen.addRecipientInfoGenerator(
                new org.bouncycastle.cms.jcajce.JceKeyTransRecipientInfoGenerator((java.security.cert.X509Certificate) recipientCert)
                        .setProvider("BC")
        );
        // Encrypt the body part with AES-128
        MimeBodyPart encryptedPart = envGen.generate(
                messageBodyPart, 
                new JceCMSContentEncryptorBuilder(CMSAlgorithm.AES128_CBC)
                        .setProvider("BC")
                        .build()
        );
        // Create a multipart to hold the encrypted content
        MimeMultipart multipart = new MimeMultipart();
        multipart.addBodyPart(encryptedPart);
        // Create the MimeMessage
        MimeMessage message = new MimeMessage(session);
        message.setFrom(new InternetAddress(username));
        message.addRecipient(Message.RecipientType.TO, new InternetAddress(recipientEmail));
        message.setSubject("Encrypted Email Example");
        message.setContent(multipart);
        // Send the message
        Transport.send(message);
        System.out.println("Encrypted email sent successfully.");
    }

Questions:

1. How to install the S/MIME extension?
2. Is the Java code I provided right or wrong?
3. How can I send a S/MIME encrypt message using Java code? Give me the steps.