function validEmail(email) {
         
    invalidChars = " /:,;"
   
    if (email == "") {
       return false
    }
    for (i=0; i<invalidChars.length; i++) {
       badChar = invalidChars.charAt(i)
       if (email.indexOf(badChar,0) > -1) {
          return false
       }
    }
    atPos = email.indexOf("@",1)
     if (atPos == -1) {
       return false
    }
    if (email.indexOf("@",atPos+1) > -1) {
       return false
    }
    periodPos = email.indexOf(".",atPos)
    if (periodPos == -1) {
       return false
    }
    if (periodPos+3 > email.length)   {
       return false
    }
    return true
 }
      

function isEmpty(s)
{   return ((s == null) || (s.length == 0))
}

function checkForm(form)
{
	     
    if ((form.email.value == "") || (isEmpty(form.email.value))){
        alert( "Please enter your email address." );
        form.email.focus();
        return false;
    }
    if (!validEmail(form.email.value)) 
    {
      alert("Please ensure you have entered a valid email address.");
      form.email.focus();
      return false;
    }
     

    return true ;
}