function isValidEmail(email)
{
  if(email.length==0){return false;}
  if(!isRestrictedToCharset(email, "abcdefghijklmnopqrstuvwxyz0123456789@.-_")){return false;}
  if(email.indexOf("@") < 1){return false;}
  else if(email.lastIndexOf(".") <= email.indexOf("@")){return false;}
  else if(email.indexOf("@") == email.length){return false;}
  else if(email.indexOf("..") >=0){return false;}
  else if(email.indexOf(".") == email.length){return false;}
  return true;
}

function isRestrictedToCharset(str, charset)
{
  var parsed = true;
  var validchars = charset;
  for (var i=0; i < str.length; i++) {
    var letter = str.charAt(i).toLowerCase();
    if (validchars.indexOf(letter) != -1)
      continue;
    parsed = false;
    break;
  }
  return parsed;
}