Just to the admin, as set in the configurations.
You are right about what's need to be done:
I have a temporary work around if you need it - it's sent when the validation link is sent, assuming the option is selected through the admin:
Just add this code to notifications.php (oc-includes\osclass)
just after the validation link and before this line " $body .= "<br/>--<br/>" . $preferences['pageTitle']; "
add the following code:
$body .= __('You can edit your item by clicking on this link') . ': <a href="' . ABS_WEB_URL . '/' . 'user.php?action=item_edit&id=' . $item['pk_i_id'] . '&secret=' . $item['s_secret'] . '" >' . ABS_WEB_URL . '/' . 'user.php?action=item_edit&id=' . $item['pk_i_id'] . '&secret=' . $item['s_secret'] . '</a><br/>';
$body .= __('You can delete your item by clicking on this this link') . ': <a href="' . ABS_WEB_URL . '/' . 'user.php?action=item_delete&id=' . $item['pk_i_id'] . '&secret=' . $item['s_secret'] . '" >' . ABS_WEB_URL . '/' . 'user.php?action=item_delete&id=' . $item['pk_i_id'] . '&secret=' . $item['s_secret'] . '</a><br/>';
Yeah.. I know.. I'm a genius

Still can't solve the problem with the header though.. I've tried a gmail server, smtp localhost - I don't think that's the problem.