An auto-responder e-mail is an email that is sent back immediately to everyone who sends an e-mail to an email address with this option enabled. The senders will get the automatic reply once their e-mails are received and you'll not need to do anything whatsoever manually. A couple of instances of using auto-responder emails are mailing an affirmation that a transaction is received and also the order will be prepared or that an individual is on holiday and won't be around for a specific time frame. In the first situation the option is enabled for a long time, while in the second one it is short-term. Even when you work with an e-mail address just for personal communication, you can use an auto-responder to let the e-mail sender know that their email has been received successfully.