function check(forma) {
    var correo = forma.mail.value;
    var correo_ck;
    correo_ck = validar(correo);

    if (correo_ck) {
       setTimeout('muestra("gracias")', 2000);
       forma.submit();
       forma.mail.value = ''; }
    else {return false;}
}

function validar(eAddr) { //hay que refinarla !!
   var goodAddr = false;
   var ndxAt = ndxDot = 0;
   ndxAt  = eAddr.indexOf("@");
   ndxDot = eAddr.indexOf(".");
   if (!eAddr) {alert("Please enter an email address");}
   else if ((ndxDot < 0) || (ndxAt < 0)) {
      alert("Your email address lacks '.' or '\@'.\nThe format is 'you\@dom.suf'");}
   else {goodAddr = true}

   return goodAddr 
}