You can get an autoresponder for emails at "SendinBlue". Not only does it offer free email marketing campaigns for an unlimited amount of subscribers, it also offers an automatic email responder which you can customise to respond to specific emails on certain conditions. The autoresponder is currently in beta at SendinBlue but you won't have any problems with it, it also offers 2000 FREE contacts that can receive automated emails and thereafter, it is only $39 per month if you need more contacts to receive automated emails, though you can have unlimited contacts for just a normal marketing campaign.
Actually a very good (equivalent) of an Autoresponder for a small business is offered for free by Anoox. They dont market it as such, but in fact it pretty much does what an Autoresponder does, and it is free. Here how to use the Anoox Autoresponder:
1- Get your friends, colleagues, etc. join Anoox, which of course they can join for free in less than 30 Seconds
2- After they join have them click on your "Follow Me" button
3- Thereafter, whenever you post a Questions, Discussion, Poll, etc. they will be Auto emailed about your posting. Just make sure to mark your posting as Private so that it wont be flagged as SPAM.