function validate_input()
{ 
  sender_name = document.form1.sender_name.value;
  sender_email = document.form1.sender_email.value;
  msubject = document.form1.msubject.value;
  mbody = document.form1.mbody.value;

  if (sender_name.length < 3){
      alert("Please enter your name");
      document.form1.sender_name.focus();
      return(false);
  }
  
  if (sender_email.length < 5 ){ 
      alert("Please enter an email address."); 
      document.form1.sender_email.focus();
      return (false);
  } 

  var emailFilter=/^.+@.+\..{2,3}$/; 
  if (!(emailFilter.test(sender_email))){ 
      alert("Please enter a valid email address."); 
      document.form1.sender_email.select();
      return (false);
  } 

 if (msubject.length<1){
      alert("Please select a feedback subject.");
      document.form1.msubject.focus();
      return (false);
  } 

 if (mbody.length<1){
      alert("Please enter the email content.");
      document.form1.mbody.focus();
      return (false);
  } 
  return(true);
}