Over the past year-and-a-half I've been actively looking for a free or reasonably priced self-hosted autoresponder solution. I came across many... from free to paid, from Wordpress plugins to self-installed scripts. They were either too expensive for my tastes, quite buggy or flat out did not perform in a reliable manner. Eventually, I somehow stumbled across Maian Responder.
This self-hosted autoresponder installs in a straight forward manner and has an easy to use front-end interface. Functionally simple without too many bells and whistles and it works fantastic. In addition, David's support is second to none.