An auto-responder is usually a predefined email, that's sent automatically as an answer to each message received in a mailbox with this function activated. The two most typical examples for employing this function are automated e-mails that one is temporarily out of the office or that an order is received successfully. An auto-responder can also be used as a common verification that the e-mail is delivered successfully, which is often something rather important in enterprise communication. The message which is delivered can be more or less anything and can be altered according to the conditions and what the auto-responder will be used for. As the option is enabled server-side, there isn’t anything you have to do by hand and you do not need an e-mail program to be enabled all the time for an automatic reply to be mailed to the person sending you an email.