Form element validation handler for #type 'email'.
Note that #maxlength and #required is validated by _form_validate() already.
function form_validate_email(&$element, &$form_state) {
$value = trim($element['#value']);
form_set_value($element, $value, $form_state);
if ($value !== '' && !valid_email_address($value)) {
form_error($element, t('The e-mail address %mail is not valid.', array(
'%mail' => $value,
)));
}
}