function mailtest(address) {
  return (/^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$/.test(address));
 }

function enrich_email() {
  var input;
  input = document.getElementsByTagName('input');
  for (i=0; i<input.length; i++) {
    if ( (input[i].getAttribute('type')=='text') &&
         (input[i].className.indexOf('email')>-1)  ) {
      input[i].onblur = function() {
        if (mailtest(this.value)==false)
          alert('Direccion de correo no valida');
       }
     }
   }
 }

window.onload = function() {
  if (DOM == 0) return;
  enrich_email();
}

var DOM;
DOM = (document.getElementById) ? 1 : 0;