function valid_email(email)
{
    if(email == ''){
        return false;
    }
    var filter  = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
    if(filter.test(email)){
        return true;
    }    
    return false;
}