$q=mysql_query("SELECT * FROM `mail` WHERE `id_user` = '$user[id]' AND `id_kont` = '$ank[id]' OR `id_user` = '$ank[id]' AND `id_kont` = '$user[id]' ORDER BY id DESC LIMIT $start, $set[p_str]");
на это:
$q=mysql_query("SELECT * FROM `mail` WHERE `id_user` = '$user[id]' AND `id_kont` = '$ank[id]' OR `id_user` = '$ank[id]' AND `id_kont` = '$user[id]' ORDER BY id LIMIT $start, $set[p_str]");