An auto-responder is a predefined e-mail message, which is sent automatically as an answer to each and every email received inside a mailbox with this option activated. The two most common examples for using this function are automatic e-mails that one is temporarily out of the office or that an order is received successfully. An auto-responder could also be used as a standard verification that the e-mail is received successfully, which is often something quite important in business e-mail correspondence. The message that's sent can be more or less anything and can be modified according to the circumstances and what the auto-responder will be employed for. As the option is activated server-side, there isn’t anything you are expected to do manually and you don't need an e-mail program to be enabled constantly for an automatic reply to be sent to the individual sending you an email.