An auto-responder is usually a predefined e-mail, that is sent automatically as an answer to each email received in a mailbox with this feature enabled. The two most typical instances for employing this function are automated e-mails that one is temporarily away from the office or that an order is received successfully. An auto-responder may also be used as a standard verification that the e-mail is received successfully, which may be something very important in enterprise communication. The message which is sent can be more or less anything and could be modified depending on the situations and what the auto-responder will be used for. As the feature is enabled server-side, there isn’t anything you have to do by hand and you do not need an email application to be active all the time for an automatic reply to be sent to the person sending you an e-mail.