function valida(){


 parte1 = document.form.email.value.indexOf("@");
 parte2 = document.form.email.value.indexOf(".");
 parte3 = document.form.email.value.length;
if (!(parte1 >= 3 && parte2 >= 6 && parte3 >= 9)) {
alert ("you must use a valid email address! Ex.: seunome@dominio.com");
document.form.email.focus();
return false;
}
}