<script>
            var nuser;
            function contaEmail(suoemail) {
                var val = document.forms.mioform1;
                var max=5  
                if(suoemail.indexOf('@')<0) {
                    nuser = suoemail.length;
                    val.suoemail.value = val.suoemail.value.substring(0,max);
                    output = nuser > max ? "Username: max 5 caratteri" : '';
                } 
                else {
                    document.getElementById('contaUserDom').innerHTML = '';
                    max =  8 + nuser + 1;                     
                    val.suoemail.value = val.suoemail.value.substring(0 ,max);
                    output = suoemail.value > max ? "Dominio: max 8 caratteri" : '';
                }
                if(output.length != 0) { 
                    document.getElementById('contaUserDom').innerHTML = (output + '');
                }
            }  
        </script>