We provide three major mailinglists. <announce@otrs.org> is a low traffic announcement mailinglist. To subcribe it visit http://lists.otrs.org/.
The second mailinglist is <otrs@otrs.org>. It is a medium to high traffic list with all sorts of questions and support to the product. To subcribe it visit http://lists.otrs.org/.
The third mailinglist is <dev@otrs.org>. It is a medium to high traffic list. The OpenTRS developers discuss various design and implementation issues here. To subcribe it visit http://lists.otrs.org/.