Here is a simple to use plugin that will not only give you the functionality of an auto-responder, but will also give you the ability to send out great looking newsletters and it's user friendly. It's called WYSIJA .. You can download it free from Wordpress.org. There is a 5 minute video from the page and when you activate the plugin, there is another video tutorial that is dead simple to understand.
WYSIJA means What you see is just awesome.
Build your list (S) and email your members anytime with terrific newsletters.