if (!$is_draft && !$form_state['values']['details']['finished']) {
    $submission = webform_get_submission($node->webform['nid'], $sid, TRUE);
    webform_submission_send_mail($node, $submission);
  }

function MODULE_mail_alter(&$message) {
  //You can do your conditional check here and depending on that
  //you can set the value of $message['send'] to false to stop the mail from being sent.
  //place the line below inside conditional loop, or else it'll stop every mail from being sent ;-)
  $message['send'] = FALSE;
}

yoursite.com/node/XXX/webform/emails

foreach ($node->webform['emails'] as $key => $email) {
    $node->webform['emails'][$key]['status'] = 1 // or 0 to disable;
  }