function checkmail(strEmail){
  validRegExp = /^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i;
  strEmail = document.forms[0].email.value;

    if (strEmail.search(validRegExp) == -1) 
   {
      alert('Por favor, informe um email válido');
      return(document.form1.email.focus());
      return false;
    } 
    return true; 
}
//isValidEmail