gistfile1.txt

public AsyncCommandImpl implements AsyncCommand {

    public void onCommand(SMTPSession session, SMTPRequest req, SMTPServerResponseCallback callback) {
     ....
     ....
     smtpClientSession.write(new SMTPRequest(...), new SMTPResponseCallback() {
         public void onResponse(SMTPResponse resp) {
              callback.onSMTPServerResponse(new SMTPResponse(resp));
         }
     }
    }
}