try {
    Transport.send(msg);
} catch (MessagingException e) {
    // When failure occurs in sending the message
}

// Acquire Transport class object
Transport transport = null;
try {
    transport = session.getTransport("smtp");
} catch (NoSuchProviderException e) {
    // When provider is not found
    // Does not occur because the SMTP provider is set up by default settings
}
try {
    // Connecting to the SMTP server
    transport.connect();
 
    // Update the header before sending
    msg.saveChanges();
 
    // Send message
    transport.sendMessage(msg, msg.getAllRecipients());
 
    // Repeated invocation of sendMessage() method when sending multiple messages. 
    // transport.sendMessage(msg2, msg2.getAllRecipients());
    // ...
} catch (MessagingException e) {
    // When connecting to the SMTP server or when an attempt to send message fails
} finally {
    try{
        // Disconnection from the SMTP server
        transport.close();
    }catch(MessagingException e){
        // When fails to disconnect server    
    }
}