The essence of the applet is the sendMsg() method, which opens a socket to port 25 of the applet source (this is the standard
SMTP port), feeds the expected SMTP header to this port, dumps the contents of a TextArea into the port (your message), then
adds the required period and QUIT.

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import java.awt.*;
import java.applet.*;
import java.net.*;
import java.io.*;

public class Mailer extends Applet {

private int SMTP_PORT = 25;
private String appletSource = "add source";

private TextArea MsgArea;
private TextField senderField, recipientField, hostField;

public void init() {

setLayout(new BorderLayout());

Panel fields = new Panel();
fields.setLayout(new GridLayout(3, 1));

Panel recPanel = new Panel();
recPanel.setLayout(new GridLayout(2, 1));
recPanel.add(new Label("Recipient"));
recipientField = new TextField("");
recPanel.add(recipientField);
fields.add(recPanel);

Panel sendPanel = new Panel();
sendPanel.setLayout(new GridLayout(2, 1));
sendPanel.add(new Label("Sender"));
senderField = new TextField("president");
sendPanel.add(senderField);
fields.add(sendPanel);

Panel hostPanel = new Panel();
hostPanel.setLayout(new GridLayout(2, 1));
hostPanel.add(new Label("Host"));
hostField = new TextField("whitehouse.gov");
hostPanel.add(hostField);
fields.add(hostPanel);

add("North", fields);

MsgArea = new TextArea();
add("Center", MsgArea);


add("South", new Button("SEND"));

}

public boolean handleEvent(Event e) {
if (e.id == Event.WINDOW_DESTROY)
System.exit(0);
return super.handleEvent(e);
}

public boolean action(Event e, Object arg) {

if (arg.equals("SEND"))
sendMsg(senderField.getText(), recipientField.getText(),
hostField.getText());
else
return super.action(e, arg);
return true;

}


private void sendMsg(String sender, String recipient, String senderHost) {

try {
Socket s = new Socket(appletSource, SMTP_PORT);
PrintStream out = new PrintStream(s.getOutputStream());
MsgArea.selectAll();
out.println("HELO " + senderHost); // SMTP doesn't verify sender host!
out.println("MAIL FROM: " + sender);
out.println("RCPT TO: " + recipient);
out.println("DATA");
out.println(MsgArea.getSelectedText());
out.println(".");
out.println("QUIT");
}
catch(Exception e) { System.out.println("Error " + e); }

} // sendMsg

} //Mailer