I would suggest you either use Aweber or Getresponse.
Both of these are the current leaders.
Another option would be to install an autoresponder script on your domain. Though this would save you a little money, I would recommend against it. Not only is it difficult to maintain, but also it would be a headache to troubleshoot if something goes wrong.
I would recommend Aweber and Getresponse. These are the best currently.
Getresponse costs $ 17.95/month. However, if you order for 1 year, it costs $145 ($70 off). See
www.getresponse.com for more details.