aweber.com currently owns the IM world. I have some experience with them and with mailchimp. This is like somewhere in between, aweber is more spammy prone while mailchimp won't allow you to auto-respond unless you buy a subscription.

Baisically, there isn't a reliable freemium service with an autoresponder. It also strucks me as "hassle free" light service i would use for medium to small size projects. Will use it soon