sendmail 에러

sendmail을 이용 신청서를 접수하려 하는데 에러가 발생합니다.

혹 아시는분 도와 주세요. 감사합니다.

public class SendMail extends HttpServlet {   
 String host= "localhost";//11,16,51,52,59
 String sender= "";// 보내는 사람 주소
 String receiver= "";//받는 사람 주소
 String topic= "";//제목
 String content= "";// 내용
 String mime= "";// 문서 타입
 public SendMail(){
 }
 public SendMail(String sender2, String receiver2, String topic2, String content2, String mime2) throws IOException{
  sender= sender2;
  receiver= receiver2;
  topic= topic2;
  content= toKR(content2);
  mime= mime2;
 }
 public boolean send() throws IOException{
        Properties props = new Properties();   
        props.put("mail.smtp.host", host);   
        Session session = Session.getDefaultInstance(props, null);   
        try {   
           Message msg = new MimeMessage(session);   
   String receiver_tmp= "";
   StringTokenizer stk= new StringTokenizer(receiver, "/");
   int stkCnt= stk.countTokens();
   InternetAddress[] address = new InternetAddress[stkCnt];
   int i4= 0;
   while(stk.hasMoreTokens()) {
    receiver_tmp= stk.nextToken();
    address[i4] = new InternetAddress(receiver_tmp);
    i4++;
   }
           msg.setRecipients(Message.RecipientType.TO, address);   
            msg.setFrom(new InternetAddress(sender));   
            msg.setSubject(topic);   
            msg.setSentDate(new Date());   
            if(mime.equals("text")) msg.setText(content); // TEXT형식   
            else msg.setContent(content,"text/html; charset=euc-kr"); // HTML형식   
            Transport.send(msg);   
      return true;
        } 
  catch (MessagingException e){   
   e.printStackTrace();   
   return false;
        }
    }   
 public static String toKR(String str1) throws UnsupportedEncodingException{
  if(str1 == null){
   return("");
  }
  return(new String(str1.getBytes("8859_1"), "KSC5601"));
 }
}